powerpc32: adds handling of _PAGE_RO

Some powerpc like the 8xx don't have a RW bit in PTE bits but a RO
(Read Only) bit.  This patch implements the handling of a _PAGE_RO flag
to be used in place of _PAGE_RW

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[scottwood@freescale.com: fix whitespace]
Signed-off-by: Scott Wood <scottwood@freescale.com>

diff --cc arch/powerpc/include/asm/pgtable-ppc32.h
Simple merge

diff --cc arch/powerpc/include/asm/pgtable.h
Simple merge

diff --cc arch/powerpc/include/asm/pte-common.h
Simple merge

diff --cc arch/powerpc/mm/pgtable_32.c
Simple merge