powerpc/8xx: Add missing SPRN defines into reg_8xx.h

Add missing SPRN defines into reg_8xx.h
Some of them are defined in mmu-8xx.h, so we include mmu-8xx.h in
reg_8xx.h, for that we remove references to PAGE_SHIFT in mmu-8xx.h
to have it self sufficient, as includers of reg_8xx.h don't all
include asm/page.h

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <oss@buserror.net>