atmel_lcdfb: don't initialize a pre-allocated framebuffer

If the user specified a fixed framebuffer address on the command line, it may
have been initialized already with a splash image or something, so we
shouldn't clear it.

Therefore, we should only initialize the framebuffer if we allocated it
ourselves.  This patch also updates the AVR32 setup code to clear the
framebuffer if it allocated it itself, i.e.  the user didn't provide a fixed
address or the reservation failed.

I've updated the at91 platform code as well so that it initializes the
framebuffer if it is located in SRAM, but I haven't tested that it actually
works.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Nicolas FERRE <nicolas.ferre@rfo.atmel.com>
Cc: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>