drm/i915/dg1: gmbus pin mapping

Add tables to map the GMBUS pin pairs to GPIO registers and port to DDC.
From spec we have registers GPIO_CTL[1-4], so we should not do the 4->9
mapping as in ICL/TGL.

The values for VBT seem wrong in BSpec. For the current boards we
actually have a 1:1 mapping.

BSpec: 49311, 49945, 20124

Cc: Aditya Swarup <aditya.swarup@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201007002210.3678024-5-lucas.demarchi@intel.com