soc/qcom: rpmh: correctly wait for TCS flush

soc/qcom: rpmh: correctly wait for TCS flush

Several bugs were discovered in the rpmh-rsc driver which collectively
meant we were never actually waiting for the TCS to flush, these were
likely missed because U-Boot runs single threaded and the RPMh had
typically processed the single command we sent by the time we went
to send the next one. However a future patch will implement rpmh read
support which requires us to properly wait for the RPMh command response
so we can return the value.

Fix these issues so we correctly ensure the TCS is done before
returning.

Link: https://patch.msgid.link/20260108-rpmh-regulator-fixes-v1-3-d1b5b300b665@linaro.org
Signed-off-by: Casey Connolly <casey.connolly@linaro.org>