disp: msm: sde: reuse cont-splash path for LE VM resource allocation

Add necessary checks during the splash init to check
& execute the splash/ramdump buffer mapping/unmapping
only for the cont-splash use-case. This would help in
reusing the same path for LE VM setup during device assign,
which does not have any splash buffer.

Change-Id: I3ce168c530c7db4b14465efa3fd87889b5f99f5b
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>