drm/i915/lnl: Add gmbus/ddc support

LNL's south display uses the same table as MTP. Check for LNL's fake PCH
to make it consistent with the other checks.

The VBT table doesn't contain the VBT -> spec mapping for LNL. Like in
other cases, uses the same as the previous platform.

Bspec: 68971, 20124
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230919192128.2045154-18-lucas.demarchi@intel.com