msm: mdss: Add battery FET regulator usage

During idle power-collapse using smart-panel, when PMIC chip goes to
sleep, it puts battery FET (batfet) to low power mode (LPM) which allows
less than 100mA current to be drawn. Since smart-panel is in self-refresh
mode, it can still draw more than 100mA current causing PMIC and MSM
reset. To fix this issue, batfet has to be kept in high power mode (HPM).
In order to keep batfet in HPM, display driver enables batfet regulator
whenever display panel is on.

Change-Id: I2f3d9f20fcf86b3147ac7396d56f93bfc08377c7
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>