Introduce pmap_remove_l3_range() and use it in two places:
(1) pmap_remove(), where it eliminates redundant TLB invalidations by
pmap_remove() and pmap_remove_l3(), and (2) pmap_enter_l2(), where it may
optimize the TLB invalidations by batching them.

Reviewed by: markj
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D12725