Change pmap_extract() and pmap_extract_and_hold() to use PG_FRAME rather than ~PDRMASK to extract the physical address of a superpage from a PDE. The use of ~PDRMASK is problematic if the PDE has PG_NX set.  Specifically, the PG_NX bit will be included in the physical address if ~PDRMASK is used.
Change pmap_extract() and pmap_extract_and_hold() to use PG_FRAME rather
than ~PDRMASK to extract the physical address of a superpage from a PDE.
The use of ~PDRMASK is problematic if the PDE has PG_NX set.  Specifically,
the PG_NX bit will be included in the physical address if ~PDRMASK is used.

Reviewed by:	peter

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase