* pmap_protect(): write back the range when doing a r/w -> r/o
transition. (Still leave the block concerned with this in
pmap_clean_page() disabled, for now.)
* pmap_pte_init_xscale(): Disable read/write-allocate for now, until
we figure out why sometimes cache lines of NULs get deposited into
file data. Also, make sure ECC protection of page table access is
disabled for now.
* xscale_setup_minidata(): Make sure the mini-data cache is configured
write-back with read/write-allocate.