drm/i915/icl: Add Voltage swing table for MG PHY DDI Buffer

This table is used for voltage swing programming sequence during DDI
Buffer initialization for MG PHY DDI Buffers on Icelake.

v2 (from Paulo):
* Fix white space issues.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@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/20180323172419.24911-5-paulo.r.zanoni@intel.com