edk2: Build only for aarch64 based machines
edk2: Build only for aarch64 based machines

helps including this BSP layer in a multi-bsp layer environment

Signed-off-by: Khem Raj <729d64b6f67515e258459a5f6d20ec88b2caf8df@gmail.com>

kraj/meta-96boards,kraj/meta-96boards,mrchapp/meta-96boards,96boards/meta-96boards,fboudra/meta-96boards