drm/i915/dp: Add support for HBR3 and TPS4 during link training

DP spec 1.4 supports training pattern set 4 (TPS4) for HBR3 link
rate. This will be used in link training's channel equalization
phase if supported by both source and sink.
This patch adds the helpers to check if HBR3 is supported and uses
TPS4 in training pattern selection during link training.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180611222655.5696-2-paulo.r.zanoni@intel.com