drm/amdgpu: Fix handling of KFD initialization failures

Remember KFD module initializaton status in a global variable. Skip KFD
device probing when the module was not initialized. Other amdgpu_amdkfd
calls are then protected by the adev->kfd.dev check.

Also print a clear error message when KFD disables itself. Amdgpu
continues its initialization even when KFD failed.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>