MAINTAINERS: Add mailing list for the interconnect API

Add a mailing list for patch reviews and discussions related to tuning
the on-chip interconnects. For now i am not expecting a lot of traffic,
so let's use the linux-pm@ list.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>