ANDROID: arm64: Wrap MPAM setup with a config option

As it turns out, there are broken firmwares out there, and an apparent
need to turn MPAM off until the firmware can be fixed.

Introduce the ARM64_MPAM config option, wrap the MPAM setup with it,
and set it as default for GKI. Non-GKI uses with broken firmwares can
have their own config fragments to deal with it.

The config option text is lifted from James Morse's git tree.

Bug: 228613614
Signed-off-by: Marc Zyngier <mzyngier@google.com>
Change-Id: Ib782aab89c826ea96dbf9ae26c16d1a4a61c41fb