BACKPORT: arm64: add support for the AMU extension v1

The activity monitors extension is an optional extension introduced
by the ARMv8.4 CPU architecture. This implements basic support for
version 1 of the activity monitors architecture, AMUv1.

This support includes:
- Extension detection on each CPU (boot, secondary, hotplugged)
- Register interface for AMU aarch64 registers

Bug: 172781912
Change-Id: I8fa585dd992213d8042e6f9ddec2cb3bcefade05
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit 2c9d45b43c39e26fd2a73f2203321cdaee98b58b)
[neeraju: Resolved minor conflicts in Kconfig, cpucaps.h, cpufeature.h]
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>