msm: mdss: dsi: validate ULPS config requests

In the current implementation, ULPS entry/exit requests are placed
whenever DSI link clocks are disabled/enabled. However, certain
optimizations can be done avoid unnecessary transitions such as for
cases when clocks are turned off briefly prior to panel
initialization/uninitialization, and then turned right back on to send
the panel on/off commands. Add these optimizations and avoid ULPS
configuration for such cases.

CRs-Fixed: 961817
Change-Id: Ie6c666b91e86697c37e0a557f9ba47811392ae90
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>