msm: mdss: Fix FB base layer pipe allocation failure

At boot time when RGB pipe is used as frame buffer base
layer, it is failing in kickoff as pipe's front buffer
has zero planes. Add check for front buffer's number
of plane in kickoff.

Change-Id: I67cefedac3ca272012eb41812caa0bce5cca637e
Signed-off-by: Pawan Kumar <pavaku@codeaurora.org>