arm64: dts: imx8mn-beacon: Configure Ethernet PHY reset and GPIO IRQ

arm64: dts: imx8mn-beacon: Configure Ethernet PHY reset and GPIO IRQ

The Ethernet PHY setup currently assumes that the bootloader will take the
PHY out of reset, but this behavior is not guaranteed across all
bootloaders. Add the reset GPIO to ensure the kernel can properly control
the PHY reset line.

Also configure the PHY IRQ GPIO to enable interrupt-driven link status
reporting, instead of relying on polling.

This ensures more reliable Ethernet initialization and improves PHY event
handling.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>