On iMX8MM EVK, there are two USB ports. Both can support USB PD, but
with USB2 has HW priority.

So we Change tcpc_pd_sink_check_charging to public function and
use it to know whether the USB tcpc is power charging.

Additional, add disable_pd to init config. So we can disable PD session
for uncharged or lower priority port.

Signed-off-by: Ye Li <ye.li@nxp.com>