arm-cci: Provide hook for writing to PMU counters

arm-cci: Provide hook for writing to PMU counters

Add a hook for writing to CCI PMU counters. This callback
can be used for CCI models which requires some extra work
to program the PMU counter values. To accommodate group writes
and single counter writes, the call back accepts a bitmask
of the counter indices which need to be programmed with the
given value.

Cc: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>