USB: host: st: fix ehci/ohci driver selection

The newly added sti ehci and ohci drivers come with a single
Kconfig entry that does not depend on either of the base drivers,
which leads to a link error when they are disabled:

drivers/built-in.o: In function `ohci_platform_init':
:(.init.text+0x14788): undefined reference to `ohci_init_driver'

To fix that, this patch introduces two separate Kconfig options
with proper dependencies, which avoids the problem and is also
more consistent with the other glue drivers.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: d1158372 ("usb: host: ohci-st: Add OHCI driver support for ST STB devices")
Cc: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>