usb: ehci-omap: Add Support for DM_USB and OF_CONTROL

The omap3.dtsi file shows the usbhshost node with two sub-nodes
for ohci and ehci.  This patch file creates the usbhshost, and
pulls the portX-mode information.  It then locates the EHCI
sub-node, and initializes the EHCI controller with the info
pulled from the usbhshost node.

There is still more to do since there isn't an actual link
between the 'phys' reference and the corresponding phy driver,
and there is no nop-xceiv driver yet.

In the meantime, the older style reference to
CONFIG_OMAP_EHCI_PHYx_RESET_GPIO is still needed to pull
the phy out of reset until the phy driver is completed and the
phandle reference is made.

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