perf arm-spe: Implement find_snapshot callback

The head pointer of the AUX buffer managed by the arm_spe_pmu.c driver
is not monotonically increasing, therefore the find_snapshot callback is
needed in order to find the trace data within the AUX buffer and avoid
wasting space in the perf.data file.

The pointer is assumed to have wrapped if the buffer contains non-zero
data at the end. If it has wrapped, the entire contents of the AUX
buffer are stored in the perf.data file. Otherwise only the data up to
the head pointer is stored.

Reviewed-by: James Clark <[email protected]>
Reviewed-by: Leo Yan <[email protected]>
Signed-off-by: German Gomez <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Garry <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Poirier <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Tested-by: Leo Yan <[email protected]>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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