net: Add Amlogic GXL MDIO Mux driver

Port the mdio-mux-meson-gxl.c Linux driver introduced in [1],
and adapt it to U-Boot.

This driver is needed to boot U-Boot with Linux DT since v6.4,
since it switched the MDIO mux from the mmio to a proper GXL driver.

[1] 9a24e1ff4326 ("net: mdio: add amlogic gxl mdio mux support")

Link: https://lore.kernel.org/r/20231213-u-boot-gxl-mdio-mux-v2-1-c56bb02a75ea@linaro.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 23ad2c2..b2d7b49 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -980,4 +980,11 @@
 	  This driver is used for the MDIO mux found on the Amlogic G12A & compatible
 	  SoCs.
 
+config MDIO_MUX_MESON_GXL
+	bool "MDIO MUX for Amlogic Meson GXL SoCs"
+	depends on DM_MDIO_MUX
+	help
+	  This driver is used for the MDIO mux found on the Amlogic GXL & compatible
+	  SoCs.
+
 endif # NETDEVICES