USB: EHCI: make ehci-orion a separate driver

With the multiplatform changes in arm-soc tree, it becomes
possible to enable the mvebu platform (which uses
ehci-orion) at the same time as other platforms that require
a conflicting EHCI bus glue. At the moment, this results
in a warning like

drivers/usb/host/ehci-hcd.c:1297:0: warning: "PLATFORM_DRIVER" redefined [enabled by default]
drivers/usb/host/ehci-hcd.c:1277:0: note: this is the location of the previous definition
drivers/usb/host/ehci-orion.c:334:31: warning: 'ehci_orion_driver' defined but not used [-Wunused-variable]

and an ehci driver that only works on one of them.

With the infrastructure added by Alan Stern in patch 3e023203
"USB: EHCI: prepare to make ehci-hcd a library module", we can
avoid this problem by turning a bus glue into a separate
module, as we do here for the orion bus glue.

Signed-off-by: Manjunath Goudar <manjunath.goudar@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>