Fix USB hub bugs: Don't allocate port EP0 until needed, otherwise run out of endpoints; using wrong pointer to access child endpoint array in a few places

STM32 RTC counter: Include enable/disable backup domain within critical section.  Per recommendtion of Alexander Oryshchenko.

STM32 F1 RTC Counter:  Now need to enable backup domain write access when setting the time.  From Darcy Gong

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.