usb: chipidea: improve kconfig 2.0

This patch provides a cleaner solution to the problem described in
commit 20a677fd ("usb: chipidea: improve kconfig").

The goal to be achieved is to force USB_CHIPIDEA=m if either
USB_EHCI_HCD=m or USB_GADGET=m.
If both are 'y' USB_CHIPIDEA may be selected to be 'm' or 'y'.

The old patch had the drawback, that USB_CHIPIDEA could be chosen as
'y' though USB_EHCI_HCD or USB_GADGET (or both) were 'm' leading to a
situation where USB_CHIPIDEA_HOST or USB_CHIPIDEA_UDC vanished from
the config options producing a compilable but dysfunctional driver.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Reviewed-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>