mdss: display: add mdp core clock to edp control

Since mdss interrupts are generated in mdp core clock domain,
mdp clock need to be enabled along with edp clocks to have edp
interrupt be delivered to edp during edp probe.

Change-Id: Idad19dddfdc2aed9efda15b28b666ac0411dbbda
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>