msm: mdss: update performance calculations to include border color

Current clock and bus scaling calculations consider only source
surface pipes to set clock rate and bus scaling factor, however
since MDP also generates pixels for border color this area also
needs to be considered for final clock and bus scaling factors
for data paths that use layer mixer.

Change-Id: I9463c01dfd0b7a301797bd036f563e15d5195dbd
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>