drm/i915/cnl: Add Port F definition.

Some Cannonlake SKUs will come with a full split between
port A and port E. This will be called port F although it
is not a 6th port, but only a split.

Note this patch alone is not sufficient for port F enabling,
it's just the first step.

v2: Fix size of dvo_ports found by Ander.
v3: Adding missing cases from intel_bios.c for Port_F
v4: Adding other missing cases and fix the commit message.
v5: Rebase on top of display headers rework.
v6 (from Paulo): improve commit message, bikeshed bit definitions.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180111180010.24357-2-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -1378,6 +1378,7 @@ static i915_reg_t skl_aux_ctl_reg(struct drm_i915_private *dev_priv,
 	case PORT_B:
 	case PORT_C:
 	case PORT_D:
+	case PORT_F:
 		return DP_AUX_CH_CTL(port);
 	default:
 		MISSING_CASE(port);
@@ -1393,6 +1394,7 @@ static i915_reg_t skl_aux_data_reg(struct drm_i915_private *dev_priv,
 	case PORT_B:
 	case PORT_C:
 	case PORT_D:
+	case PORT_F:
 		return DP_AUX_CH_DATA(port, index);
 	default:
 		MISSING_CASE(port);