drm/amd/display: DMCU FW loading from PSP

Update the programming sequence to allow DMCU firmware to be loaded by
PSP. This code detects whether the firmware is loaded and does a check
to verify the expected interface version and checks for correct response
from micro controller.

Added registry key method to allow force loading of firmware from kernel
mode driver for test purposes. This is old method of firmware loading
without PSP.

Moved some init sequences into dc/dmcu.

Changed loading sequence to initialize IRAM after firmware completely
loaded. Firmware will now disable features that use IRAM
until initialized.

Signed-off-by: Anthony Koo <anthony.koo@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>