drm: Add DPCD definitions for DP 1.4 FEC feature

Forward Error Correction is supported on DP 1.4.
This patch adds corresponding DPCD register definitions.

v2: Add dri-devel mailing list to the CC list(Jani)

v3: Change names, add missing masks (Manasi)

v4: Add missing shifts to mask (Manasi)

v5: Arrange the definitions in ascending order
of the address (Jani)

v6: remove unnecessary definitions. Add missing masks,
add "/* 1.4 */" to offset definitions. (Jani)

Cc: dri-devel@lists.freedesktop.org
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1518636498-20921-1-git-send-email-anusha.srivatsa@intel.com