USB: EHCI: DT support for generic bus glue

USB: EHCI: DT support for generic bus glue

This lets us use the ehci-platform driver on platforms without special
requirements for their ehci controllers. In particular, this is true
for the vt8500/wm8x50 platforms, which currently have a separate
driver that causes problems with multiplatform configurations.

Tested-by: Tony Prisk <[email protected]>
Tested-by: Peter Vasil <[email protected]>
Acked-by: Alan Stern <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>