arm64: Add stubs so kernel can at least link

Signed-off-by: Jaroslaw Pelczar <jarek@jpelczar.com>
Change-Id: I2476a6346c912c4aa0c26e4f3720ea2c2690b669
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1857
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>