Revert "Revert "msm: mdss: enable pll regulator during phy on sequence""

This reverts commit 0a4917a2.
This change is causing corruption issue on msm8996 dual dsi
cmd mode panel.

Change-Id: Iba316b22c7cc211c384f5b5204e0b6f11d169d8a
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>