drm/i915/icl: Update FIA supported lane count for hpd.

In ICL, Flexible IO Adapter (FIA) muxes data and clocks of USB 3.1,
tbt and display controller. In DP alt mode FIA configure the
number of lanes and will be used apart from DPCD read to calculate max
available lanes for DP enablement.

v2 (from Paulo): Simple rebase.

Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com> (v1).
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
[Paulo: significant rewrite of the patch.]
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180725002813.6938-4-paulo.r.zanoni@intel.com