drm/amdkfd: add amdgpu_device entry to kfd_dev

Patch series to remove kgd_dev struct and replace all instances with
amdgpu_device objects.

amdgpu_device needs to be declared in kgd_kfd_interface.h to be visible
to kfd2kgd_calls.

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>