video: deferred io with physically contiguous memory

Extend the deferred io code from only supporting vmalloc()ed frame
buffer memory to support both vmalloc()ed and physically contiguous
frame buffer memory.

The sh_mobile_lcdcfb hardware does not support scatter gather so
we need physically contiguous memory to back our frame buffer.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: Jaya Kumar <jayakumar.lkml@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>