dt-bindings: arm: Add support for DSB MSR register

Add property "qcom,dsb-msrs-num" to support DSB(Discrete Single
Bit) MSR(mux select register) for TPDM. It specifies the number
of MSR registers supported by the DSB TDPM.

Signed-off-by: Tao Zhang <quic_taozha@quicinc.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/1695882586-10306-13-git-send-email-quic_taozha@quicinc.com