Revert r240317 to prevent leaking pmap entries

Revert r240317 to prevent leaking pmap entries

Subsequent to r240317, kmem_free() was replaced with kva_free() (r254025).
kva_free() releases the KVA allocation for the mapped region, but no longer
clears the pmap (pagetable) entries.

An affected pmap_unmapdev operation would leave the still-pmap'd VA space
free for allocation by other KVA consumers.  However, this bug easily
avoided notice for ~7 years because most devices (1) never call
pmap_unmapdev and (2) on amd64, mostly fit within the DMAP and do not need
KVA allocations.  Other affected arch are less popular: i386, MIPS, and
PowerPC.  Arm64, arm32, and riscv are not affected.

Reported by:	Don Morris <dgmorris AT earthlink.net>
Submitted by:	Don Morris (amd64 part)
Reviewed by:	kib, markj, Don (!amd64 parts)
MFC after:	I don't intend to, but you might want to
Sponsored by:	Dell Isilon
Differential Revision:	https://reviews.freebsd.org/D25689