msm: mdss: turn off the phy during idle pc only if panel supports

Commit ff19fe24e621ae5dc90f7e45fe4cfe159a647d15 ("mdss:
dsi: turn off phy power supply during static screen")
turns off the dsi phy during idle pc for phy rev 2.0. DSI
lanes are in floating state after dsi phy power off and
all panels may not be able to handle it. This change
allows to turn on the feature based on panel capability.

Change-Id: I9b166df254128a8a53c567f88971779b9ad0f36c
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>