drm/msm/mdp5: Drop clock names with "_clk" suffix

We have upstream bindings (msm8916) that have the "_clk" suffix in the
clock names. The downstream bindings also require it.

We want to drop the "_clk" suffix and at the same time support existing
bindings. Update the MDP5 code with the the msm_clk_get() helper to
support both old and new clock names.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>