[U-Boot] TI xHCI updates

[Dan Murphy]

This patch series contains the following changes

- Moves the xhci-omap.h to a common location
- Fixes a compilation issue on OMAP5 when xHCI is defined when patch
"usb: new board-specific USB init interface" is applied
- Moves the TI USB PHY code out of the xhci-omap.c file and into
a new file called drivers/usb/phy/omap_usb_phy.c
- Enables the dra7xx xHCI controller
- Enables the AM437x xHCI controller
- Move OMAP5 MAC creation out of USB and into misc_init so that usbethaddr is
set on each boot or else the kernel sets a random MAC.