MAINTAINERS: Add myself as cpuidle reviewer

I've been reviewing cpuidle changes, for governors in particular, for
the last couple of years and will continue to do so.

Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/71f63cb7-2d9b-49a3-9b04-a47e2edef5e0@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: cloehle

MAINTAINERS

@@ -6554,6 +6554,7 @@ F:	rust/kernel/cpu.rs
 CPU IDLE TIME MANAGEMENT FRAMEWORK
 M:	"Rafael J. Wysocki" <rafael@kernel.org>
 M:	Daniel Lezcano <daniel.lezcano@linaro.org>
+R:	Christian Loehle <christian.loehle@arm.com>
 L:	linux-pm@vger.kernel.org
 S:	Maintained
 B:	https://bugzilla.kernel.org