cpu: add HPDS, LOR, PAN detection for arm64

This CL gets ID_AA64MMFR1_EL1, Memory Model Feature Register 1, and
grabs HPDS, LOR, PAN features from its bits.

Fixes golang/go#75472.

Change-Id: Ic04b109d79aceba9b3b1d3a1ea514fcf132007c5
GitHub-Last-Rev: f938ff468bca49cc7863aa26e7a880eec2823bb4
GitHub-Pull-Request: golang/sys#263
Reviewed-on: https://go-review.googlesource.com/c/sys/+/704075
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>