Fix the spelling of EFI_PAGE_SIZE

We assume EFI_PAGE_SIZE is the same as PAGE_SIZE, however this may not
be the case. Use the former when working with a list of pages from the
UEFI firmware so the correct size is used.

This will be needed on arm64 where PAGE_SIZE could be 16k or 64k in the
future. The other architectures have been updated to be consistent.

Reviewed by: imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34510