drm/i915: Simplify the link training functions
Split the prepare, link training, fallback-handling steps into their own
functions for clarity and as a preparation for the upcoming LTTPR
changes.
While at it also:
- Unexport and inline intel_dp_set_idle_link_train(), which is used at a
single place.
- Add some documentation to functions that are exported or that can use
a better description about which part of the LT sequence they
implement.
v2: (Ville)
- Unexport/inline intel_dp_set_idle_link_train()
- Make the documentation of
intel_dp_prepare_link_train()/intel_dp_stop_link_train() more accurate
wrt. HW specific details.
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/20201007170917.1764556-3-imre.deak@intel.com