drm/amdkfd: Support enumerating non-GPU devices

Modify kfd_topology_enum_kfd_devices(..) function to support non-GPU
nodes. The function returned NULL when it encountered non-GPU (say CPU)
nodes. This caused kfd_ioctl_create_event and kfd_init_apertures to fail
for Intel + Tonga.

kfd_topology_enum_kfd_devices will now parse all the nodes and return
valid kfd_dev for nodes with GPU.

Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>