drm/i915/icl: Add register definition for DFLEXDPMLE

DFLEXDPMLE register is required to tell the FIA hardware which
main links of DP are enabled on TCC Connectors. FIA uses this
information to program PHY to Controller signal mapping.
This register is applicable in both TC connector's Alternate mode
as well as DP connector mode.

v2:
* Remove _ICL prefix since the reg is first introduced
in ICL (Paulo)
* s/ICL/icl in commit message (Lucas)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Madhav Chauhan <madhav.chauhan@intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@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/1527275032-4555-1-git-send-email-manasi.d.navare@intel.com