OMAP: DSS2: Use MIPI DSI enums from include/video/mipi_display.h

MIPI DSI Transaction types and DCS commands are currently defined as
macros in dsi.c and panel-taal.c, remove these and replace them with
enum members defined in include/video/mipi_display.h.

Signed-off-by: Archit Taneja <archit@ti.com>
[tomi.valkeinen@ti.com: reformatted the commit message]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>