ARM: 7357/1: perf: fix overflow handling for xscale2 PMUs

ARM: 7357/1: perf: fix overflow handling for xscale2 PMUs

commit 3f31ae121348afd9ed39700ea2a63c17cd7eeed1 upstream.

xscale2 PMUs indicate overflow not via the PMU control register, but by
a separate overflow FLAG register instead.

This patch fixes the xscale2 PMU code to use this register to detect
to overflow and ensures that we clear any pending overflow when
disabling a counter.

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