gicv3: Add a verbose message for unknown tables

Add a message under bootverbose when we find a gicv3 its table type
that is unknown.

Reviewed by: gallatin, imp
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D41553

(cherry picked from commit 629734783de5212ea2a7cdc6a8fb7cf6834b1344)