drm/msm/sde: populate drm modes before mode set in continuous splash

The order of the modes exposed by the DRM connector may differ from
the order they were probed by the display driver. To ensure the same
mode to be selected by the SDM, always populate the DRM connector modes
before selecting the mode to configure in continuous splash.

Change-Id: I821efab328a616faebbc648d553777453cc3d44e
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>