The Cortex-A53 supports the ARMv8-A Architecture. The following commands were used to compile this code on the Raspberry Pi 3. Please note, you will need to pull bootcode.bin and start.elf from the Raspberry Pi github master branch.
$ arm-none-eabi-gcc -O2 -mfpu=neon-vfpv4 -mfloat-abi=hard -march=armv8-a -mtune=cortex-a53 \ -nostartfiles pulse.c -o kernel.elf
$ arm-none-eabi-objcopy kernel.elf -O binary kernel7.img
$ cp kernel7.img kernel.img