Cleanup to use most x86_64 UEFI code for all archs

mk/aarch64-unknown-uefi.mk

mk/x86-unknown-none.mk

mk/x86_64-unknown-uefi.mk

src/main.rs

src/os/uefi/arch/aarch64/mod.rs

src/os/uefi/arch/x86_64/memory_map.rs

src/os/uefi/arch/x86_64/mod.rs

src/os/uefi/memory_map.rs

src/os/uefi/mod.rs

src/os/uefi/video_mode.rs