usb: host: remove tilegx platform glue

The tile architecture is getting removed, so the ehci and ohci platform
glue drivers are no longer needed. In case of ohci, this is the last
one to define a PLATFORM_DRIVER macro, so we can remove even more.

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