On the Allwinner's A31 SoC the reset line connected to the EHCI IP has to
be deasserted for the EHCI block to be usable.

Add support for an optional reset controller that will be deasserted on
power off and asserted on power on.
Signed-off-by: NBoris BREZILLON <boris.brezillon@free-electrons.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: NHans de Goede <hdegoede@redhat.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>