update pmac_defconfig

enable all relevant options in common_defconfig,
so it can serve as a compiletest for PPC_MULTIPLATFORM configuration
Signed-off-by: Olaf Hering <olh@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>