drm/i915/tc: Add a mode for the TypeC PHY's disconnected state

A follow-up change will start to disconnect/re-connect PHYs around AUX
transfers and modeset enable/disables. To prepare for that add a new
TypeC PHY disconnected mode, to help tracking the TC-cold blocking power
domain status (no power domain in disconnected state, mode dependent
power domain in connected state).

v2: Move the !disconnected mode and phy-owned asserts in
    __intel_tc_port_lock() later in the patchset, when the asserts will
    hold. (Jose)

Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210929132833.2253961-3-imre.deak@intel.com