usb: ehci-omap: Move omap_ehci_hcd_init to omap_ehci_probe

usb: ehci-omap: Move omap_ehci_hcd_init to omap_ehci_probe

The OMAP3 hierarchy has the ehci node as a sub-node of the
usbhshost. The usbhshost node contains an ohci and an ehci
subnode.  The configuration of the ehci belongs in the
EHCI node and not its parent.  Move it to the proper probe.

usb start
  starting USB...
  Bus ehci@48064800: USB EHCI 1.00
  Bus usb_otg_hs@480ab000: Port not available.
  scanning bus ehci@48064800 for devices... 3 USB Device(s) found
       scanning usb for storage devices... 1 Storage Device(s) found

Signed-off-by: Adam Ford <aford173@gmail.com>