net: phy: add driver for MaxLinear MxL86110 PHY

net: phy: add driver for MaxLinear MxL86110 PHY

Add support for the MaxLinear MxL86110 Gigabit Ethernet PHY, a low-power,
cost-optimized transceiver supporting 10/100/1000 Mbps over twisted-pair
copper, compliant with IEEE 802.3.

The driver implements basic features such as:
- Device initialization
- RGMII interface timing configuration
- Wake-on-LAN support
- LED initialization and control via /sys/class/leds

This driver has been tested on multiple Variscite boards, including:
- VAR-SOM-MX93 (i.MX93)
- VAR-SOM-MX8M-PLUS (i.MX8MP)

Example boot log showing driver probe:
[    7.692101] imx-dwmac 428a0000.ethernet eth0:
	PHY [stmmac-0:00] driver [MXL86110 Gigabit Ethernet] (irq=POLL)

Signed-off-by: Stefano Radaelli <stefano.radaelli21@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250521212821.593057-1-stefano.radaelli21@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>