soc: qcom: rpmpd: Allow RPMPD driver to be loaded as a module

soc: qcom: rpmpd: Allow RPMPD driver to be loaded as a module

This patch allow the rpmpd driver to be loaded as a permenent
module. Meaning it can be loaded from a module, but then cannot
be unloaded.

Ideally, it would include a remove hook and related logic, but
apparently the genpd code isn't able to track usage and cleaning
things up? (See: https://lkml.org/lkml/2019/1/24/38)

So making it a permenent module at least improves things slightly
over requiring it to be a built in driver.

Cc: Todd Kjos <tkjos@google.com>
Cc: Saravana Kannan <saravanak@google.com>
Cc: Andy Gross <agross@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Rajendra Nayak <rnayak@codeaurora.org>
Cc: linux-arm-msm@vger.kernel.org
Acked-by: Saravana Kannan <saravanak@google.com>
Tested-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Link: https://lore.kernel.org/r/20200326224459.105170-2-john.stultz@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>