usb: phy: mxs: add usb charger type detection

mxs phy has data pin contact and usb charger detector blocks which
can be controlled by software to detect charger type for SDP, CDP and
DCP.

Reviewed-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Li Jun <jun.li@nxp.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>