apm821xx: Add support for the Cisco Meraki MX60/MX60W

This patch adds support for the Cisco Meraki MX60/MX60W Security
Appliance. Flashing information can be found at
https://github.com/riptidewave93/LEDE-MX60

Specs are as follows:
AppliedMicro APM82181 SoC at 800MHz
1GiB NAND - Samsung K9K8G08U0D
512MB DDR RAM - 4x Nanya NT5TU128M8GE-AC
Atheros AR8327-BL1A Gigabit Ethernet Switch
1x USB 2.0 Port

More info can be found at https://wiki.openwrt.org/toh/meraki/mx60

Cc: Christian Lamparter <chunkeey@gmail.com>

Signed-off-by: Chris Blake <chrisrblake93@gmail.com>

target/linux/apm821xx/base-files/lib/upgrade/platform.sh

@@ -16,7 +16,8 @@ platform_check_image() {
 		return $?;
 		;;
 
-	mr24)
+	mr24|\
+	mx60)
 		merakinand_do_platform_check $board "$1"
 		return $?;
 		;;
@@ -38,7 +39,8 @@ platform_pre_upgrade() {
 	local board=$(apm821xx_board_name)
 
 	case "$board" in
-	mr24)
+	mr24|\
+	mx60)
 		merakinand_do_upgrade "$1"
 		;;