drm/i915/icl: implement the tc/legacy HPD {dis,}connect flows

drm/i915/icl: implement the tc/legacy HPD {dis,}connect flows

Unlike the other ports, TC ports are not available to use as soon as
we get a hotplug. The TC PHYs can be shared between multiple
controllers: display, USB, etc. As a result, handshaking through FIA
is required around connect and disconnect to cleanly transfer
ownership with the controller and set the type-C power state.

This patch implements the flow sequences described by our
specification. We opt to grab ownership of the ports as soon as we get
the hotplugs in order to simplify the interactions and avoid surprises
in the user space side. We may consider changing this in the future,
once we improve our testing capabilities on this area.

v2:
 * This unifies the DP and HDMI patches so we can discuss everything
   at once so people looking at random single patches can actually
   understand the direction.
 * I found out the spec was updated a while ago. There's a small
   difference in the connect flow and the patch was updated for that.
 * Our spec also now gives a good explanation on what is really
   happening. As a result, comments were added.
 * Add some more comments as requested by Rodrigo (Rodrigo).
v3:
 * Downgrade a DRM_ERROR that shouldn't ever happen but we can't act
   on in case it does (Chris).

BSpec: 21750, 4250.
Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180801173441.9789-1-paulo.r.zanoni@intel.com