drm/amdgpu: add UMSCH firmware header definition
Add firmware header definition for UMSCH.
Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Veerabadhran Gopalakrishnan <Veerabadhran.Gopalakrishnan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
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