coresight-tpdm: Remove the unnecessary lock

Remove the unnecessary lock "CS_{UN,}LOCK" in TPDM driver. This
lock is only needed while writing the data to Coresight registers.

Signed-off-by: Tao Zhang <quic_taozha@quicinc.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/1695882586-10306-2-git-send-email-quic_taozha@quicinc.com