Fix superpage promotion on ARM with respect to RO/RW and wired attributes

Fix superpage promotion on ARM with respect to RO/RW and wired attributes

It was possible to create RW superpage mapping even if
the base pages were RO due to wrong setting of the prot
flag passed to pmap_map_section().
Promotion attempt should be canceled in case of attributes
mismatch between any two base pages. Since we still use
pv_flags to maintain permission to write (PVF_WRITE) and
wired status (PVF_WIRED) for a page, it is also necessary
to take those variables into account.