PM / Domains: Add DT file to MAINTAINERS

Add the power_domain.txt DT file to MAINTAINERS, otherwise
get_maintainers.pl doesn't pick the right set of maintainers for changes
to the DT file.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NUlf Hansson <ulf.hansson@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -5493,6 +5493,7 @@ L:	linux-pm@vger.kernel.org
 S:	Supported
 F:	drivers/base/power/domain*.c
 F:	include/linux/pm_domain.h
+F:	Documentation/devicetree/bindings/power/power_domain.txt
 
 GENERIC UIO DRIVER FOR PCI DEVICES
 M:	"Michael S. Tsirkin" <mst@redhat.com>