gicv3: In its_init_cpu_lpi record each cpu's PENDBASER

When we're using the preallocated memory for gicv3, record each cpu's
PENDBASER where we'd normally allocate memory for it. Make sure that
memory is in the excluded list and map the PA to VA and store that, to
mimic what we do with the allocation case.

Sponsored by: Netflix
Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D44037