drm/amd/display: Indirect buffer transport for FAMS2 commands

drm/amd/display: Indirect buffer transport for FAMS2 commands

[Why]
The quantity and duration of FAMS2 commands are set to increase
in future products. This necessitates the implementation of a new
mechanism for chaining commands together, allowing all commands
to be processed within a single transaction.

[How]
The indirect buffer acts as a shared buffer on the driver side,
mapped to DMUB's internal CW7 address. Its source address and
size are sent through mailbox command to DMUB, triggering the
transaction.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Oleh Kuzhylnyi <okuzhyln@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>