sh: Couple kernel and user write page perm bits for CONFIG_X2TLB

pte_write() should check whether the permissions include either the user
or kernel write permission bits. Likewise, pte_wrprotect() needs to
remove both the kernel and user write bits.

Without this patch handle_tlbmiss() doesn't handle faulting in pages
from the P3 area (our vmalloc space) because of a write. Mappings of the
P3 space have the _PAGE_EXT_KERN_WRITE bit but not _PAGE_EXT_USER_WRITE.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>