drm/i915/icl: Fix the DP Max Voltage for ICL

drm/i915/icl: Fix the DP Max Voltage for ICL

On clock recovery this function is called to find out
the max voltage swing level that we could go.

However gen 9 functions use the old buffer translation tables
to figure that out. ICL uses different set of tables for eDP
and DP for both Combo and MG PHY ports. This patch adds the hook
for ICL for getting this information from appropriate buf trans tables.

v5 (from Paulo):
* New rebase after changes to earlier patches.
v4:
* Rebase.
v3:
* Follow the coding conventions here
(https://cgit.freedesktop.org/drm-intel/tree/Documentation/process/codin
g-style.rst#n191) (Paulo)
v2:
* Rebase after patch that adds voltage check inside buf trans
function (Rodrigo)

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@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/20180328215803.13835-9-paulo.r.zanoni@intel.com