Build boot1.efi for arm64

We can use the boot1 code directly with a few Makefile changes.
Allow the IL bit to be clear in one case

In an exception from the same level when the ISV bit (bit 24) is set
the IL bit (bit 25) may not be set as is the case with QEMU.
Implement pmap_unwire and pmap_remove_write

These are based on the amd64 version with only the small mapping
code as we don't support super pages.