drm/omap: dsi: pass vc and channel to various functions

To start fixing the issues related to channels and vcs described in the
previous commit, pass vc and/or channel to various functions which will
need it do properly handle different DSI channels and VCs.

No functional changes.

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/20201215104657.802264-67-tomi.valkeinen@ti.com