dt-bindings: arm-pmu: Add PMU compatible strings for Apple M2 cores

The PMUs on the Apple M2 cores avalanche and blizzard CPU are compatible
with M1 ones. As on M1 we don't know exactly what the counters count so
use a distinct compatible for each micro-architecture.
Apple's PMU counter description omits a counter for M2 so there
is some variation on the interpretation of the counters.

Signed-off-by: Janne Grunau <j@jannau.net>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Hector Martin <marcan@marcan.st>
Link: https://lore.kernel.org/r/20230214-apple_m2_pmu-v1-1-9c9213ab9b63@jannau.net


Signed-off-by: Will Deacon <will@kernel.org>