drm/amd/display: Fix DMUB meta offset for new load method

[Why]
The new metadata offset is located at the end of the firmware binary
without any additional padding.

Firmware state is currently larger than 1024 bytes so new firmware state
will hang when trying to access any data above 1024 bytes.

[How]
Specify the correct offset based on legacy vs new loading method.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>