Documentation: trace: Add documentation for TPDM and TPDA

Add documentation for the TPDM and TPDA under trace/coresight.

Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230117145708.16739-9-quic_jinlmao@quicinc.com