drm/dp: Add definitions for TPS4 bits and macros to check the support

DP 1.4 spec adds a TPS4 training pattern sequence required for
HBR3. This patch adds the corresponding bit definitions in
MAX_DOWNSPREAD register and TRAINING_PATTERN_SET and
inline functions to check if this bit is set and for selecting
a proper TRAINING_PATTERN_MASK that changed to 0x7 on
DP spec 1.4

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/1516660991-20697-2-git-send-email-manasi.d.navare@intel.com