ar71xx: add support for RB951Ui-2nD

This patch adds support for the MikroTik RouterBOARD hAP
https://routerboard.com/RB951Ui-2nD

Specifications:
- SoC: Qualcomm QCA9531 (650MHz)
- RAM: 64MB
- Storage: 16MB NOR SPI flash
- Wireless: builtin QCA9531, 2x2:2
- Ethernet: 5x100M (1 PoE in, 1 PoE out)
- USB: Type A

Signed-off-by: Thibaut VARENE <hacks@slashdirt.org>

target/linux/ar71xx/base-files/lib/upgrade/platform.sh

@@ -344,6 +344,7 @@ platform_check_image() {
 	pb42|\
 	pb44|\
 	rb-941-2nd|\
+	rb-951ui-2nd|\
 	rb-mapl-2nd|\
 	routerstation-pro|\
 	routerstation|\
@@ -617,6 +618,7 @@ platform_pre_upgrade() {
 
 	case "$board" in
 	rb-941-2nd|\
+	rb-951ui-2nd|\
 	rb-mapl-2nd)
 		;;
 	rb*|\
@@ -654,6 +656,7 @@ platform_do_upgrade() {
 
 	case "$board" in
 	rb-941-2nd|\
+	rb-951ui-2nd|\
 	rb-mapl-2nd)
 		PLATFORM_DO_UPGRADE_COMBINED_SEPARATE_MTD=1
 		platform_do_upgrade_combined "$ARGV"