msm: mdss: update DSI PHY panel timing dt parsing logic

In current implementation there are two entries in DSI
panel specific dt file for specifying panel timing parameters.
But in case only one entry is specified in panel dt, then if the
first entry is not there in dt, driver is returning failure
and because of this the second entry is not getting parsed at all.
Update the parsing logic so that driver parses both the entries
to get proper dsi panel timing parameters.

Change-Id: I1774421fd9686de123cb669a745ac110fe8667da
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>