For virtual addresses use fixed page frame without AMD SEV reduction.

For virtual addresses use fixed page frame without AMD SEV reduction.

When running as a SEV guest, page frame mask is calculated from the
CPUID provided "physical address bit reduction".  The amd64 pmap
code uses the variable pg_frame instead of the defined PG_FRAME
0x000ffffffffff000.
There was one instance in pmap code where pg_frame was applied to
virtual address, not physical address.  On some machines the address
bit reduction is rather large with six bits.  So the calculated
pg_frame is 0x00003fffffe00000.  However, on amd64 VM_MAX_ADDRESS
is defined as 0x00007fbfdfeff000.  Masking a such large address
with pg_frame caused havoc.  Therefore, when masking virtual
addresses, still use PG_FRAME.

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