usb: ehci-mx6: implement ofdata_to_platdata

Implement ofdata_to_platdata to set the type to host or device.
 - Check "dr-mode" property.
 - If there is no "dr-mode", check phy_ctrl for i.MX6
   and phy_status for i.MX7

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefano Babic <sbabic@denx.de>