drm/i915/tc: Add TC PHY hook to get the PHY HPD live status

Add a table of TC PHY hooks which can be used to call platform specific
TC PHY handlers, replacing the corresponding if ladders.

Add the hook to retrieve the PHY's HPD live status. Move the common part
fixing up the VBT legacy port flag to the generic helper.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323142035.1432621-9-imre.deak@intel.com