drm/mipi-dsi: Introduce mipi_dsi_dcs_write_seq macro

A helper macro that can be used to simplify sending DCS commands.
It is useful in scenarios like panel initialization which can sometimes
involve sending lot of DCS commands.

Signed-off-by: Joel Selvaraj <jo@jsfamily.in>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/BY5PR02MB700952493EEB6F0E77DC8416D9DF9@BY5PR02MB7009.namprd02.prod.outlook.com