ps3fb: don't keep the borders for non-fullscreen modes in XDR memory

Don't keep the borders for non-fullscreen modes in XDR memory:
  - Extract ps3fb_sync_image()
  - Work around the alignment restrictions of L1GPU_CONTEXT_ATTRIBUTE_FB_BLIT
    by using an offset with L1GPU_CONTEXT_ATTRIBUTE_DISPLAY_FLIP
  - Only copy the visible part of the screen on every vblank
  - Always put the real frame buffer at the start of video memory
  - Clear fullscreen DDR memory on mode change

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>