microchipsw: lan969x: add Microchip EV23X71A

microchipsw: lan969x: add Microchip EV23X71A

Microchip EV23X71A is a LAN9696 based EVB.

Specifications:
* CPU: Microchip LAN9696 switch SoC
* DRAM: 1GB DDR4
* Storage:
	* 2MB QSPI NOR
	* 4GB eMMC
* Networking:
	* 24 x 10/100/1000 RJ45 via LAN8814 Quad PHY-s over QSGMII
	* 4 x 100/1000/2500/5000/10000 SFP+ ports
	* 1 x 10/100/1000 management RJ45 via LAN8840 PHY over RGMII (U-Boot too)
* USB: 1 x USB2.0 Type-A
* Management via USB-C (MCP2200):
	* UART @ 115200 baud
	* GPIO-s for bootstrap, reset and clock selection
* DIP switch for boostrap configuration
* LED-s:
	* 2 per networking port (Green and Yellow)
	* Green status LED
	* Yellow reset LED
* Hard reset button
* Power:
	* 12V DC barrel jack
	* 48/56V DC screw terminal
	* Selectable via toggle switch
* PTP support:
	* Sync-E DPLL ZL30732B to generate the board required clocks
	* Two SMAs for PTP and two for Station clock inputs and outputs
	* Two ITU-T G.8275-compliant RS-422 interfaces for PTP applications
* External PoE:
	* Option for PoE add-on, like EV14Y36A (IEEE 802.3af/at/bt Type 4
	standard com-pliant)
* Option for external CPU control via SPI and PCIe

Installation instructions:

1. Connect to UART via the USB-C port
2. Connect the management port
3. Boot and interrupt U-Boot
4. TFTP the OpenWrt initramfs image and boot it
5. SCP the OpenWrt eMMC GPT image to a running OpenWrt initramfs to /tmp
openwrt-microchipsw-lan969x-microchip_ev23x71a-squashfs-emmc-gpt.img.gz

And decompress it via:
gzip -d /tmp/openwrt-microchipsw-lan969x-microchip_ev23x71a-squashfs-emmc-gpt.img.gz

6. Wipe eMMC with:
dd if=/dev/zero of=/dev/mmcblk0 bs=1M

7. Flash OpenWrt eMMC image with:
dd if=/tmp/openwrt-microchipsw-lan969x-microchip_ev23x71a-squashfs-emmc-gpt.img
of=/dev/mmcblk0

After a restart OpenWrt will boot, and then regular sysupgrade can be used
for upgrades.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>