FROMLIST: soc: qcom: rpmh: Allow RPMH driver to be loaded as a module

This patch allow the rpmh 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
the rpmh driver is fairly core to the system, so once its loaded
with almost anythign else to get the system to go, the dependencies
are not likely to ever also be removed.

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/20200326224459.105170-3-john.stultz@linaro.org/T/#u
Change-Id: I865f3ad0baa3b84bc0ea321df88238a3a89101a8