thermal: cpu_cooling: Add MAINTAINERS entry

None of the patches are reaching Viresh or Daniel directly as
get_maintainers doesn't report us as maintainers. Looks like file header
or history of commits isn't able to do that properly.

Add a separate entry for cpu_cooling driver in MAINTAINERS.

Acked-by: Eduardo Valentin <edubezval@gmail.com>
Acked-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Acked-by: Amit Daniel Kachhap <amit.kachhap@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>