drivers: qcom: rpmh: remove rpmh_flush export

drivers: qcom: rpmh: remove rpmh_flush export

rpmh_flush() was exported with the idea that an external entity
operation during CPU idle would know when to flush the sleep and wake
TCS. Since, this is not the case when defining a power domain for the
RSC. Remove the function export and instead allow the function to be
called internally.

Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/1580736940-6985-3-git-send-email-mkshah@codeaurora.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>