amd64 pmap: Use INVPCID_CTXGLOB on Ryzen processors

Recent AMD Ryzen processors support a limited form of the invpcid
instruction, even when they do not support PCID functionality. In
particular, they support the type 2 form of the instruction, what we
call INVPCID_CTXGLOB. This is faster than toggling PGE in cr4.

Reviewed by: kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D51565