mdss: display: add 16 bits length dcs command support

current implemtation only supports 8 bits of dcs length.
This patch adds support of 16 bits dcs length as specified
at dcs standard. Therefore all dcs related tx/rx functions
are needed be updated. In addition, all dsi panel dtsi files
are need to be updated too since it contains dcs header.

Change-Id: Icc72a5076e1b181a9bdeb2479e877022c4dc9b22
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>