msm: mdss: Do not program DSI PLL registers from DSI controller

MDSS DSI driver currently programs certain DSI PLL registers as
part of the DSI PHY off sequence. This is incorrect and could
lead to some unexpected errors such as DSI PLL getting turned off
while the branch clocks are still on. Fix this by removing all
such register programming.

Change-Id: Ie1e88cd18de6b8ef8804f7a2b34b8b8282166c96
CRs-Fixed: 509801
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>