net: ravb: Make reset controller support mandatory

On the RZ/G3S SoC the reset controller is mandatory for the IP to work.
The device tree binding documentation for the ravb driver specifies that
the resets are mandatory. Based on this, make the resets mandatory also in
driver for all ravb devices.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>