drm/i915/dmc: Introduce DMC_FW_MAIN

This is a prep patch for Pipe DMC plugging.

Add dmc_info struct in intel_dmc to have all common fields
shared between all DMC's in the package.
Add DMC_FW_MAIN(dmc_id 0) to refer to the blob.

v2: Remove dmc_offset and start_mmioaddr from dmc_info struct (Jose)

Cc: Souza, Jose <jose.souza@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210621191415.29823-2-anusha.srivatsa@intel.com