MAINTAINERS: add maintainer for tools/power/cpupower

Based on discussions with Rafael J. Wysocki, cpupower is need of an
active maintainer. I decided to on take the task of maintaining this
tool.

Patches will flow through the pm sub-systems to the mainline.
Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Acked-by: Thomas Renninger <trenn@suse.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -3636,6 +3636,8 @@ F:	drivers/cpufreq/arm_big_little_dt.c
 
 CPU POWER MONITORING SUBSYSTEM
 M:	Thomas Renninger <trenn@suse.com>
+M:	Shuah Khan <shuahkh@osg.samsung.com>
+M:	Shuah Khan <shuah@kernel.org>
 L:	linux-pm@vger.kernel.org
 S:	Maintained
 F:	tools/power/cpupower/