kernel/cpu: add cpu_frequency()

implement on x86 with APERFMPERF.

Change-Id: Ia484854c76dee76c5447983de15800a25d791d39
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3213
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

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>