soc: xilinx: Move power-domain driver to the genpd dir

To simplify with maintenance let's move the xilinx power-domain driver to
the new genpd directory. Going forward, patches are intended to be managed
through a separate git tree, according to MAINTAINERS.

Cc: Michal Simek <michal.simek@amd.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/genpd/Makefile

@@ -12,3 +12,4 @@ obj-y					+= starfive/
 obj-y					+= sunxi/
 obj-y					+= tegra/
 obj-y					+= ti/
+obj-y					+= xilinx/

drivers/genpd/xilinx/Makefile

+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_ZYNQMP_PM_DOMAINS)		+= zynqmp-pm-domains.o

drivers/soc/xilinx/Makefile

 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_ZYNQMP_POWER)	+= zynqmp_power.o
-obj-$(CONFIG_ZYNQMP_PM_DOMAINS) += zynqmp_pm_domains.o
 obj-$(CONFIG_XLNX_EVENT_MANAGER)	+= xlnx_event_manager.o