drm/amdkfd: replace/remove remaining kgd_dev references

Remove get_amdgpu_device and other remaining kgd_dev references aside
from declaration/kfd struct entry and initialization.

Signed-off-by: Graham Sider <Graham.Sider@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>