samples: net: Add nucleo_g431rb specific files to run echo with T1S ETH

This development board - i.e. nucleo_g431rb (STM32G491) with MicroE's
T1S LAN8651 module are used to test the eth_lan865x driver.

Test HW:
- nucleo_g491re development board from STM
- Microe LAN8651 module (GPIO reset used)
- LAN8670-USB dongle with debian12 as host

Build:
west build -p always -b nucleo_g431rb samples/net/sockets/echo_server/ \
	-- -DCONF_FILE=boards/nucleo_g431rb.conf

Test on host PC (one needs to first build echo-client program from
net-tools):
while :; do ./echo-client -r -i enx001ec0d1cc4d  192.168.3.3; sleep 1; \
	ping -c3 192.168.3.3; done

Signed-off-by: Lukasz Majewski <lukma@denx.de>

samples/net/sockets/echo_server/boards/nucleo_g431rb.conf

@@ -0,0 +1,52 @@
+# Generic networking options
+CONFIG_NETWORKING=y
+CONFIG_NET_UDP=y
+CONFIG_NET_TCP=n
+CONFIG_NET_IPV6=n
+CONFIG_NET_IPV4=y
+CONFIG_NET_SOCKETS=y
+CONFIG_NET_SOCKETS_POSIX_NAMES=y
+CONFIG_POSIX_MAX_FDS=4
+CONFIG_NET_CONNECTION_MANAGER=y
+
+# Kernel options
+CONFIG_MAIN_STACK_SIZE=2048
+CONFIG_ENTROPY_GENERATOR=y
+CONFIG_TEST_RANDOM_GENERATOR=y
+CONFIG_INIT_STACKS=y
+
+# Logging
+CONFIG_NET_LOG=n
+CONFIG_LOG=n
+CONFIG_NET_STATISTICS=n
+CONFIG_PRINTK=n
+
+# Network buffers
+CONFIG_NET_PKT_RX_COUNT=4
+CONFIG_NET_PKT_TX_COUNT=4
+CONFIG_NET_BUF_RX_COUNT=24
+CONFIG_NET_BUF_TX_COUNT=24
+CONFIG_NET_CONTEXT_NET_PKT_POOL=y
+
+# IP address options
+CONFIG_NET_MAX_CONTEXTS=2
+CONFIG_NET_MAX_CONN=2
+
+# Network shell
+CONFIG_NET_SHELL=n
+CONFIG_SHELL=n
+
+# Network application options and configuration
+CONFIG_NET_CONFIG_SETTINGS=y
+CONFIG_NET_CONFIG_NEED_IPV4=y
+CONFIG_NET_CONFIG_MY_IPV4_ADDR="192.168.3.3"
+CONFIG_NET_CONFIG_PEER_IPV4_ADDR="192.168.3.1"
+
+# How many client can connect to echo-server simultaneously
+CONFIG_NET_SAMPLE_NUM_HANDLERS=1
+
+# LAN865x T1S driver specific
+CONFIG_NET_L2_ETHERNET=y
+# CONFIG_NET_PROMISCUOUS_MODE=y
+CONFIG_ETH_LAN865X=y
+CONFIG_NET_BUF_DATA_SIZE=64

samples/net/sockets/echo_server/boards/nucleo_g431rb.overlay

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2023 DENX Software Engineering GmbH
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&spi1 {
+      eth0: lan865x@0{
+		compatible = "microchip,lan865x";
+		reg = <0>;
+
+		int-gpios = <&arduino_header 13 GPIO_ACTIVE_LOW>; /* D7 */
+		rst-gpios = <&arduino_header 14 GPIO_ACTIVE_LOW>; /* D8 */
+
+		local-mac-address = [00 19 05 00 00 01];
+
+		spi-max-frequency = <25000000>;
+
+                /* PLCA settings */
+                plca-enable;
+                plca-node-id = <1>;
+                plca-node-count = <8>;
+                plca-burst-count = <0x0>;
+                plca-burst-timer = <0x80>;
+                plca-to-timer = <0x20>;
+
+		status = "okay";
+	};
+};