drm: read boolan flag to enable static splash

The change will read the bool flag from the DT
and enable or disable the drm boot splash support based
on the entry made or not.

Change-Id: I353685aac2ca9d98bda31441e6ff6dde364d8a52
Signed-off-by: Shubham Talekar <stalek@codeaurora.org>