genpd: Create a new subsystem directory to host genpd providers

There are currently ~60 users of the genpd provider interface, which
implementations are sprinkled across various subsystems. To simplify with
maintenance let's create a new subsystem (drivers/genpd) and start moving
the providers in there.

My intention is also to host a git tree to collect and to get the patches
tested/integrated through the linux-next tree. Ideally this should release
some of the burden on the soc maintainers.

Note that, I will of course require acks/reviews from the current platform
maintainers, hence the MAINTAINERS file needs to be updated accordingly for
each genpd provider that is moved into the new genpd subsystem.

Signed-off-by: Ulf Hansson <[e-mail]>

MAINTAINERS

···
 F:	drivers/base/power/domain*.c
 F:	include/linux/pm_domain.h
 
+GENERIC PM DOMAIN PROVIDERS
+M:	Ulf Hansson <[e-mail]>
+L:	[e-mail]
+S:	Supported
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/linux-pm.git
+F:	drivers/genpd/
+
 GENERIC RESISTIVE TOUCHSCREEN ADC DRIVER
 M:	Eugen Hristev <[e-mail]>
 L:	[e-mail]

drivers/Makefile

···
 
 # SOC specific infrastructure drivers.
 obj-y				+= soc/
+obj-$(CONFIG_PM_GENERIC_DOMAINS)	+= genpd/
 
 obj-y				+= virtio/
 obj-$(CONFIG_VDPA)		+= vdpa/

drivers/genpd/Makefile

···
+# SPDX-License-Identifier: GPL-2.0-only