USB ehci: replace mach header with plat

Replace the mach/usb.h with plat/usb.h

Cc: linux-usb-devel@lists.sourceforge.net
Signed-off-by: Thomas Weber <weber@corscience.de>
Acked-by: Felipe Balbi <felipe.balbi@nokia.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>