fsl-diu-fb: update Freescale DIU driver to use page_alloc_exact()

Update the Freescale DIU driver to use page_alloc_exact() to allocate a
DMA buffer.  This also eliminates the rheap-based memory allocator.  We
can do this now because commit 6ccf61f9

 allows us to allocate 8MB
physically- contiguous memory blocks.

[akpm@linux-foundation.org: fix printk warnings]
Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>