usb: exynos: do not include plat/usb-phy.h

The definitions have moved to include/linux/usb/samsung-usb-phy.h,
and plat/usb-phy.h is unavailable from drivers in a multiplatform
configuration.

Also fix up the plat/usb-phy.h header file to use the definitions
from the new header instead of providing a separate copy.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>