usb: ehci-mx6: Fix bus enumeration for iMX7 SoCs

usb: ehci-mx6: Fix bus enumeration for iMX7 SoCs

This fixes the issues with calculation of controller indexes in
ehci_usb_bind() for iMX7, as USB controllers on iMX7 SoCs aren't
placed next to each other, and their addresses incremented by 0x10000.

Example of USB nodes for iMX7S/D:

usbotg1: usb@30b10000 {
    compatible = "fsl,imx7d-usb", "fsl,imx27-usb";
    reg = <0x30b10000 0x200>;
           ^^^^^^^^^^
....
usbotg2: usb@30b20000 {
    compatible = "fsl,imx7d-usb", "fsl,imx27-usb";
    reg = <0x30b20000 0x200>;
           ^^^^^^^^^^
....

usbh: usb@30b30000 {
    compatible = "fsl,imx7d-usb", "fsl,imx27-usb";
    reg = <0x30b30000 0x200>;
           ^^^^^^^^^^
....

Which was leading to usb enumeration issues:
Colibri iMX7 # usb start
starting USB...
Bus usb@30b10000: USB EHCI 1.00
Bus usb@30b20000: probe failed, error -22
scanning bus usb@30b10000 for devices... 1 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found

Fixes: 501547cec1("usb: ehci-mx6: Fix bus enumeration for DM case")
Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>