amdgpu: detect if we are using atomfirmware or atombios for vbios (v2)

Supposedly atomfirmware rom header is 3.3 atombios is 1.1.

v2: rebased on newer kernel

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>