macfb annotations and compiler warning fix

Add some __iomem annotations. Remove some volatile qualifiers to fix 
several compiler warnings: "passing arg 1 of `iounmap' discards qualifiers 
from pointer target type".

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>