ARM: 7315/1: perf: add support for the Cortex-A7 PMU

Cortex-A7 implements an ARMv7-compatible PMU compliant with the PMUv2
architecture specification.

This patch adds support for the PMU to the ARM perf backend.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>