soc: qcom: rpmh-rsc: Factor "tcs_reg_addr" and "tcs_cmd_addr" calculation

We can make some of the register access functions more readable by
factoring out the calculations a little bit.

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20200415095953.v3.1.Ic70288f256ff0be65cac6a600367212dfe39f6c9@changeid


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>