drm/i915: Rename DP link training functions

The link training functions had confusing names. The start function
actually does the clock recovery phase of the link training, and the
complete function does the channel equalization. So call them that
instead. Also, every call to intel_dp_start_link_train() was followed
by a call to intel_dp_complete_link_train(), so add a new start
function that calls clock_recory and channel_equalization.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>