cpu: imx8: reimplement get cpu count

Return 4 is not correct on i.MX8DX/DXL/8QM and etc. we need to count
available cpu node with device_type "cpu".

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
1 file changed