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 me...

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.