drm/bridge: tc358767: add link disable function

Currently we have tc_main_link_setup(), which configures and enabled the
link, but we have no counter-part for disabling the link.

Add tc_main_link_disable, and rename tc_main_link_setup to
tc_main_link_enable.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528082747.3631-11-tomi.valkeinen@ti.com