arm64: cpufeature: discover CPU support for MPAM

arm64: cpufeature: discover CPU support for MPAM

ARMv8.4 adds support for 'Memory Partitioning And Monitoring' (MPAM)
which describes an interface to cache and bandwidth controls wherever
they appear in the system.

Add support to detect MPAM. Like SVE, MPAM has an extra id register that
describes some more properties, including the virtualisation support,
which is optional. Detect this separately so we can detect
mismatched/insane systems, but still use MPAM on the host even if the
virtualisation support is missing.

MPAM needs enabling at the highest implemented exception level, otherwise
the register accesses trap. The 'enabled' flag is accessible to lower
exception levels, but its in a register that traps when MPAM isn't enabled.
The cpufeature 'matches' hook is extended to test this on one of the
CPUs, so that firmware can emulate MPAM as disabled if it is reserved
for use by secure world.

Secondary CPUs that appear late could trip cpufeature's 'lower safe'
behaviour after the MPAM properties have been advertised to user-space.
Add a verify call to ensure late secondaries match the existing CPUs.

(If you have a boot failure that bisects here its likely your CPUs
advertise MPAM in the id registers, but firmware failed to either enable
or MPAM, or emulate the trap as if it were disabled)

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241030160317.2528209-4-joey.gouly@arm.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>