msm: mdss: check dcs_cmd_by_left for tear_on and tear_off

"dcs_cmd_by_left" indicates that dcs commands can be only sent
for left DSI controller. Tear_on and Tear_off should not be send
to right controller when above flag is set. This change fixes the
tear_on and tear_off APIs with input validation.

CRs-Fixed: 728424
Change-Id: Ia4e37456bf4377f7dc4c7a3c1d929c06420b05e4
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>