FROMLIST: soc: qcom: rpmhpd: Allow RPMHPD driver to be loaded as a module

This patch allow the rpmhpd 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?

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

Feedback would be appreciated!

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
Signed-off-by: John Stultz <john.stultz@linaro.org>
Link: https://lore.kernel.org/lkml/20200326224459.105170-4-john.stultz@linaro.org/T/#u
Change-Id: I11e436a8a2452cd741c33bd1e2805e1b5e33ae3e