usb: host: ehci-st: Inform the reset framework that our reset line may be shared

On the STiH410 B2120 development board the ST EHCI IP shares its reset
line with the OHCI IP.  New functionality in the reset subsystems forces
consumers to be explicit when requesting shared/exclusive reset lines.

Acked-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Lee Jones <lee.jones@linaro.org>