gicv3: Report PENDBASE when bootverbose

Report some stats about PENDBASE when we're running under
bootverbose. We don't do this by default because experience has been
excess output in this routine hangs the system.

Sponsored by: Netflix
Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D44036

(cherry picked from commit b4368e83891ed9eba72c0ceccf25f7642f2bad40)