coresight: tmc: dump system memory content only when needed

Calling tmc_etf/etr_dump_hw() is required only when operating from
sysFS.  When working from Perf, the system memory is harvested
from the AUX trace API.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>