fbdev: da8xx/omap-l1xx: implement double buffering

This work includes the following:

- Implement handler for FBIO_WAITFORVSYNC ioctl.

- Allocate the data and palette buffers separately.  A consequence of
  this is that the palette and data loading is now done in different
  phases.  And that the LCD must be disabled temporarily after the palette
  is loaded but this will only happen once after init and each time the
  palette is changed.  I think this is OK.

- Allocate two (ping and pong) framebuffers from memory.

- Add pan_display handler which toggles the LCDC DMA registers between
  the ping and pong buffers.

Signed-off-by: Martin Ambrose <martin@ti.com>
Cc: Chaithrika U S <chaithrika@ti.com>
Cc: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>