coresight: etm4x: Fix accesses to TRCPROCSELR

coresight: etm4x: Fix accesses to TRCPROCSELR

TRCPROCSELR is not implemented if the TRCIDR3.NUMPROC == 0. Skip
accessing the register in such cases.

Cc: stable@vger.kernel.org
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20201127175256.1092685-7-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>