Write protect base page after superpage demotion so that it may repromote

When clearing the modification status of the superpage, one of the
base pages produced during demotion should be marked as write disabled.
The intention is that subsequent write access may repromote.
In the current implementation this was done wrong as write permission was
granted instead of forbidden.

Approved by:	cognet (mentor)
Approved by:	re
Implement pmap_advise() for ARMv6/v7 pmap module

Apply the given advice to the specified range of addresses within the
given pmap. Depending on the advice, clear the referenced and/or
modified flags in each mapping. Superpage within the given range will
be demoted or destroyed.

Reviewed by:	alc
Approved by:	cognet (mentor)
Approved by:	re
Fix GCC build error when building for ARMv6

Apply theravens's idea to move __strong_reference
macros into the proper ifdef section.

Approved by:	cognet (mentor)
Approved by:	re