Thermal: Add Linux/Thermal subsystem info in MAINTAINER file

All the changes made to the generic thermal layer, or platform thermal
drivers that make use of the thermal layer, should be sent to
linux-pm@vger.kernel.org for discussion.

And as the maintainer, I will only apply the patches that have been sent
to linux-pm@vger.kernel.org.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>