ARM: 6070/1: perf-events: add support for xscale PMUs

The perf-events framework for ARM only supports v6 and v7 cores.

This patch adds support for xscale v1 and v2 PMUs to perf, based on the
OProfile drivers in arch/arm/oprofile/op_model_xscale.c

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