atmel_lcdfb: fix initialization of a pre-allocated framebuffer

Fix initialization of framebuffer not calling ioremap_writecombine() function
and not using internal SRAM for at91sam9rl.

This is a little rework of the "Don't initialize a pre-allocated framebuffer"
patch that corrects the call to ioremap_writecombine() function.

It also cuts the use of internal SRAM for at91sam9rl : it is a bit small
for a framebuffer.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>