Existing helpers add support upto HBR2. This patch
adds support for HBR3 rate (8.1 Gbps) introduced as
part of DP 1.4 specification.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1516660991-20697-1-git-send-email-manasi.d.navare@intel.com