pmap arm64: fixing pmap_invalidate_range

It seems that if range within one page is given this page will not be
invalidated at all. Clean it up.

Submitted by: Dominik Ermel <der@semihalf.com>
Obtained from: Semihalf
Sponsored by: Cavium
Reviewed by: wma, zbb
Approved by: cognet (mentor)
Differential Revision: https://reviews.freebsd.org/D5569