msm: mdss: change SMP allocations for chroma decimation

When decimation is used, the chroma components are not down sampled in
order to prevent quality loss. This means that we need to consider this
extra pixels that are being fetched from memory for buffer latency (SMPs)
and bus bandwidth.

Change-Id: I9f05e4ece9240b787a8e2b3b3f69eec86d68b2b3
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>