drm/omap: dsi: rename dsi_display_* functions

The function names have evolved to be very confusing, and bunch of them
have "display" in them even if the function doesn't deal with display as
such (e.g. dsi_display_enable which just enables the DSI interface).
Rename them by dropping the "display".

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-79-tomi.valkeinen@ti.com