ARM: vexpress: Remove A9 PMU compatible values for non-A9 platforms

The ARM perf core code used to rely on the pmu node being
compatible with "arm,cortex-a9-pmu", even when the PMUs
of the different Cortex-A processors are not really
compatible... This is no longer required and actually
became harmful, so remove all the offending values
from Versatile Express DTS files.

Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>