clk: msm: mdss: handle continuous splash cases in DSI 12nm PLL driver

Register the DSI 12nm PLL VCO clock with the linux clock driver
for proper handoff of DSI PLL clocks for continuous splash screen during
bootup. For command mode panels, execute the DSI re-lock sequence
during boot-up to enable DSI PLL since DSI PHY is already programmed
in APPS bootloader.

Change-Id: Ieeadfcac2206631d0f278c018a601a5f5fc98727
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>