arm64: dts: freescale: imx8mm-var-som: Update FEC support with MaxLinear PHY

arm64: dts: freescale: imx8mm-var-som: Update FEC support with MaxLinear PHY

Update the FEC Ethernet controller on the i.MX8MM VAR-SOM to match the
latest SOM hardware revision using the integrated MaxLinear MXL86110 PHY.

Add the PHY VDDIO supply regulator, adjust reset timings and add a
pinctrl sleep state for low-power operation.

The PHY LED signals originate on the SOM, but the actual LEDs are part
of the carrier implementation (RJ45 connector). Move the LED
configuration to the Symphony carrier device tree, matching the
evaluation board LED wiring.

Wake-on-LAN via magic packet is not supported at the VAR-SOM level and
is therefore not enabled in the SOM device tree nor in the official
evaluation carrier board configuration (symphony).
Designs requiring WoL support may enable it in their own carrier-specific
device trees if properly integrated at the hardware level.

Signed-off-by: Stefano Radaelli <stefano.r@variscite.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>