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 <[e-mail]>
Cc: Saravana Kannan <[e-mail]>
Cc: Andy Gross <[e-mail]>
Cc: Bjorn Andersson <[e-mail]>
Cc: Rajendra Nayak <[e-mail]>
Cc: [e-mail]
Acked-by: Saravana Kannan <[e-mail]>
Tested-by: Bjorn Andersson <[e-mail]>
Reviewed-by: Bjorn Andersson <[e-mail]>
Signed-off-by: John Stultz <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bjorn Andersson <[e-mail]>

drivers/soc/qcom/Kconfig

···
 	  for the voltage rail.
 
 config QCOM_RPMPD
-	bool "Qualcomm RPM Power domain driver"
-	depends on QCOM_SMD_RPM=y
+	tristate "Qualcomm RPM Power domain driver"
+	depends on QCOM_SMD_RPM
 	help
 	  QCOM RPM Power domain driver to support power-domains with
 	  performance states. The driver communicates a performance state

drivers/soc/qcom/rpmpd.c

···
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/pm_domain.h>
 #include <linux/of.h>
···
 	{ .compatible = "qcom,qcs404-rpmpd", .data = &qcs404_desc },
 	{ }
 };
+MODULE_DEVICE_TABLE(of, rpmpd_match_table);
 
 static int rpmpd_send_enable(struct rpmpd *pd, bool enable)
 {
···
 	return platform_driver_register(&rpmpd_driver);
 }
 core_initcall(rpmpd_init);
+
+MODULE_DESCRIPTION("Qualcomm Technologies, Inc. RPM Power Domain Driver");
+MODULE_LICENSE("GPL v2");