usb: dwc3: meson-g12a: get the reset as shared

In order to support the Amlogic GXL/GXM SoCs, the reset line must
be handled as shared since also used by the PHYs.

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>