Don't forget to clean BSS in ARM64 locore
Fix minor typo in address space length in ARM64 locore

The value should be 39 bits when TnSZ is 25.
Enable other fsops for ARM64 loader

DOSFS will be useful to boot from USB stick, etc.
Add support for the fdt command in the EFI loader

Reviewed by: Ed Maste <emaste@freebsd.org>
Add support to get the DTB from UEFI

Reviewed By: Ed Maste <emaste@freebsd.org>
Implement efisfs_strategy

It doesn't provide a block device so just return EIO as net_strategy does
Support arm64 with an external copy of clang