arch/aarch64: first implementation

arch/aarch64/arch-cpu.cc

arch/aarch64/arch-cpu.hh

arch/aarch64/arch-setup.cc

arch/aarch64/arch-setup.hh

arch/aarch64/arch-switch.hh

arch/aarch64/arch-thread-state.hh

arch/aarch64/arch.hh

arch/aarch64/arm-clock.cc

arch/aarch64/arm-clock.hh

arch/aarch64/backtrace.cc

arch/aarch64/bitops.h

arch/aarch64/boot.S

arch/aarch64/elf-dl.S

arch/aarch64/entry.S

arch/aarch64/exceptions.hh

arch/aarch64/loader.ld

arch/aarch64/macros.S

arch/aarch64/math.cc

arch/aarch64/preboot.S

arch/aarch64/preboot.ld