drm/i915/dg1: Load DMC

Add support to load DMC v2.0.2 on DG1

While we're at it, make TGL use the same GEN12 firmware size definition
and remove obsolete comment.

Bpec: 49230

v2: do not replace GEN12_CSR_MAX_FW_SIZE (from José)
    and replace stale comment

Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Atwood <matthew.s.atwood@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/20201014191937.1266226-7-lucas.demarchi@intel.com