USB: EHCI: make ehci-vt8500 a separate driver

With the multiplatform changes in arm-soc tree, it becomes
possible to enable the vt8500 platform 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:1277:0: warning: "PLATFORM_DRIVER" redefined [enabled by default]
drivers/usb/host/ehci-hcd.c:1257:0: note: this is the location of the previous definition
drivers/usb/host/ehci-omap.c:319:31: warning: 'ehci_hcd_omap_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 vt8500 bus glue.

Signed-off-by: Manjunath Goudar <manjunath.goudar@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Tony Prisk <linux@prisktech.co.nz>
Cc: Alexey Charkov <alchark@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>