dt-bindings: firmware: qcom,scm: Add optional interrupt

Add an interrupt specification to the bindings to support the wait-queue
feature on SM8450 SoCs.

Signed-off-by: Guru Das Srinagesh <quic_gurus@quicinc.com>
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230113161114.22607-2-quic_sibis@quicinc.com