net: fec: Add stop mode support on i.MX8DX/i.MX8QP

net: fec: Add stop mode support on i.MX8DX/i.MX8QP

Add additional machines that requires communication to the SC firmware
to set the GPR bit required for stop mode support.

NXP i.MX8DX (fsl,imx8dx) is a low end version of i.MX8QXP (fsl,imx8qxp),
while NXP i.MX8QP (fsl,imx8qp) is a low end version of i.MX8QM
(fsl,imx8qm).

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260105152452.84338-1-francesco@dolcini.it
Signed-off-by: Jakub Kicinski <kuba@kernel.org>