kboot: Print UEFI memory map

If we can read the UEFI memory map, go ahead and print the memory map.
While the kernel prints this with bootverbose, having it at this stage
is useful for debugging other problems.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D44287

(cherry picked from commit a9cd3b675e243648aa681bc6ce1bf3e788be88c8)