ARM: perf: add PMUv2 common event definitions

The PMUv2 specification reserves a number of event encodings
for common events.

This patch adds these events to the common event enumeration
in preparation for PMUv2 cores, such as Cortex-A15.

Acked-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>