MAINTAINERS: update Qualcomm maintainer

As Ramon has been inactive for some time now, add myself and Neil
Armstrong to maintain Qualcomm efforts going forwards.

Add Sumit Garg who maintains several Qualcomm platforms as reviewer.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>