Fix an error introduced into stm32_pwr_enablebkp().  That function must preserve the previous state of backup domain access on return.

Add support for the new DMA2D features to the STM32F429i-Disco LTDC configuration.  From Marco Krahl.

Defines a second interface for the dma2d controller.  Controlling both LTDC and DMA2D was unpractical from the programmers view because both controllers are to different. LTDC only controls the display visibility but the DMA2D controller changes the content of the frame buffer (buffer of the layer).

The main features are:

1. DMA2D interface
   Supports the nuttx pixel formats:
   - FB_FMT_RGB8
   - FB_FMT_RGB24
   - FB_FMT_RGB16_565
   Dynamic layer allocation during runtime for the supported formats
   - The number of allocatable layer can be configured.
   Supported dma2d operation:
   - blit (Copy content from source to destination layer) also works with
     selectable area.
   - blend (Blend two layer and copy the result to a destination layer wich can
     be a third layer or one of the source layer) also works with selectable
     area.
   - fillarea (Fill a defined area of the whole layer with a specific color)

As a result of that the dma2d controller can't transfer data from the core coupled memory, CCM is disabled but usable by the ccm allocator. Currently the ccm allocator is used for allocating the layer structurei only. For the dma memory (layers frame buffer) memory is allocated from heap 2 and 3.

2. LTDC interface

   I have changed the api for the currently non implemented operations:
   - blit (Copy content from a dma2d layer to an ltdc layer) also works with
     selectable area.
   - blend (Blend two dma2d layer and copy the result to a destination ltdc
     layer) also  works with selectable area.

     Note! ltdc layer is a layer referenced by the ltdc interface. dma2d layer
     is a layer referenced by the dma2d interface.

     One of the most important questions for me was, How can i flexible use an
     ltdc layer with the dma2d interface, e.g. as source layer for dma2d
     operations?
     Get the layer id of the related dma2d layer by a special flag when using
     getlid() function of the ltdc interface and use the layer id to reference
     the specific dma2d layer by the dma2d interface.

     The ltdc coupled dma2d layers are predefined and can't be dynamically
     allocated of freed. They use the same frame buffer memory and the same
     color lookup table.

   Changes:
   - layer internal format of the clut table
   - interrupt handling for register reload (vertical vblank) instead using
     waiting loop
   - small fixes and refactoring

From Marco Krahl.

SAM3/4 and SAMV7 UART:  The IMR register is read-only.  This means that sam_restoreints() does not actually re-enable UART interrupts.

A side-effect of changing serial settings via TERMIOS (such as tcsetattr) is that serial interrupts were being left disabled.  This is not a problem if the serial configuration is changed when there are no open references to the serial device.  In that case, serial interrupts are disabled and will not be enabled enabled until the serial device is first opened.  But it is fatal if the serial device is already opened and if there is a task waiting to receive data.  In that case, the side-effect of disabling interrupts is fatal:  That task is then left hanging with interrupts disabled.

Implements CONFIG_TIME_EXTENDED as we discussed relative to providing the last 3 members of the tm struct and support for filling them in and even using the wday in the STM32 RTC. From David Sidrane.

Add conditional logic so that people who use F1 don't have to be bother with meaningless RTC MAGIC settings

SAMV7:  Apparently the data sheet is wrong, SDRAM clocking must be enabled at the PMC or the SDRAM does not work!  The data sheet says that there is no clock control for SDRAMC

More renaming: up_lcdinitialize->board_lcd_initialize, up_lcdgetdev->board_lcd_getdev, up_lcduninitialize->board_lcd_uninitialize