efi: libstub: install boot-time memory map as config table

efi: libstub: install boot-time memory map as config table

Expose the EFI boot time memory map to the kernel via a configuration
table. This is arch agnostic and enables future changes that remove the
dependency on DT on architectures that don't otherwise rely on it.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>