Recheck the link state after a passing link training, with a 2 sec delay
to account for cases where the link goes bad following the link training
and the sink doesn't report this via an HPD IRQ.

The delayed work added here will be also used by a later patch after a
failed link training to try to retrain the link with unchanged link
params before reducing the link params.

v2: Don't flush an uninitialized delayed work (on HDMI-only DDI ports).
v3:
- Move the helpers to a new intel_encoder.c file, rename them
  accordingly. (Ville)
- Add the work to intel_encoder instead of intel_digital_port.
- Call the encoder specific link check function via an encoder hook.
- Flush the link check work during encoder destroy from
  intel_dp_encoder_flush_work().
- Flush the link check work during encoder suspend as well.
v4: Call intel_encoder_link_check_init() with a valid encoder pointer.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240610181428.2955658-1-imre.deak@intel.com