drm/i915: Relocate intel_dp_program_link_training_pattern()

intel_dp_program_link_training_pattern() clearly belongs in
intel_dp_link_training.c. Make it so.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210318161015.22070-4-ville.syrjala@linux.intel.com