ehci-mx6: Update EHCI driver to support OTG0 on i.MX7ULP

The ULP has two USB controllers. These two controllers have similar NC
registers layout as i.MX7D. But OTG0 uses UTMI PHY simliar as i.MX6, not
the integrated PHY on i.MX7D. The OTG1 needs off-chip HSIC PHY or ULPI PHY
to work.

This patch only supports OTG0 with UTMI PHY.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>