drm/amd/display: Make DMCUB bss/data firmware blob optional

[Why]
By moving everything out of .data into the other regions we can drop
the requirement for the second blob and unify it all into the inst/const
blob.

[How]
We need to still support the blob being there and not being there for
backwards compatibility.

Look for the DMCUB metadata section in the end of the inst/const blob
instead of bss/data is missing.

Clear CW2 if we don't have the data blob so we don't hang when
transitioning between data blob/blobless firmwares.

Don't memcpy the blob into CW2 region if it doesn't exist.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>