msm: mdss: Fix the race condition on phy regulator control

mdss_dsi_phy_init() controls the phy regulator. If mdss_dsi_ulps_config_sub
is invoked at that time, it will cause unexpected behavior like
clock control failure. mdss_dsi_phy_init() is invoked by mdss_dsi_on() which
is for unblank. To avoid this problem, mdss_dsi_on() is protected with
ctrl_pdata->ulps_lock.

Change-Id: Ib2dc0f49f6f15f7a9cdc5218ca0e9fe13b9e0ae4
Signed-off-by: Devin Kim <dojip.kim@lge.com>