drm/i915/tc: Add generic TC PHY connect/disconnect handlers

Add generic handlers to connect/disconnect a PHY.

Setting the TC mode to the target mode deducted from the HPD state and -
if connecting to this mode fails - falling back to connecting to the
default (TBT) mode are common to all platforms; move the logic for this
from the ICL specific connect / disconnect handlers to the generic ones.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323142035.1432621-12-imre.deak@intel.com