perf: qcom_l2: fix column exclusion check

The check for column exclusion did not verify that the event being
checked was an L2 event, and not a software event.
Software events should not be checked for column exclusion.
This resulted in a group with both software and L2 events sometimes
incorrectly rejecting the L2 event for column exclusion and
not counting it.

Add a check for PMU type before applying column exclusion logic.

Fixes: 21bdbb71

 ("perf: add qcom l2 cache perf events driver")
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>