common: Create (e)MMC image with redundant root filesystems

This image contains:

- A partition to hold bootloader config ("aux").

- Two redundant copies of the FIT framed rootfs (which will be
  upgradable by RAUC from within Infix).

- A partition to store critical configuration data ("cfg")

- A partition to store data created dynamically by Infix ("var")

board/common/genimage.cfg

@@ -0,0 +1,64 @@
+
+image aux.ext4 {
+	mountpoint = "/aux"
+	temporary = true
+	size = 2M
+
+	ext4 {
+		label = "aux"
+	}
+}
+
+image cfg.ext4 {
+	empty = true
+	temporary = true
+	size = 16M
+
+	ext4 {
+		label = "cfg"
+	}
+}
+
+image var.ext4 {
+	empty = true
+	temporary = true
+	# 44M - 24k (GPT backup)
+	size = 45032k
+
+	ext4 {
+		label = "var"
+	}
+}
+
+image mmc.img {
+	size = 512M
+	hdimage {
+		partition-table-type = "gpt"
+	}
+
+	partition aux {
+		offset = 2M
+		image = "aux.ext4"
+	}
+
+	partition primary {
+		image = "rootfs.itb"
+		size = 224M
+	}
+
+	partition secondary {
+		image = "rootfs.itb"
+		size = 224M
+	}
+
+	partition cfg {
+		image = "cfg.ext4"
+	}
+
+	partition var {
+		image = "var.ext4"
+	}
+}
+
+# Silence genimage warnings
+config {}

board/common/mkmmc.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+
+set -e
+
+common=$(dirname $(readlink -f "$0"))
+root=$BUILD_DIR/genimage.root
+tmp=$BUILD_DIR/genimage.tmp
+
+
+mkdir -p $root/aux
+cp -f $BINARIES_DIR/rootfs.itbh $root/aux/primary.itbh
+cp -f $BINARIES_DIR/rootfs.itbh $root/aux/secondary.itbh
+cp -f $BINARIES_DIR/uboot-env.bin $root/aux/uboot.env
+
+rm -rf $tmp
+
+genimage \
+    --rootpath $root \
+    --tmppath  $tmp \
+    --inputpath $BINARIES_DIR \
+    --outputpath $BINARIES_DIR \
+    --config $common/genimage.cfg

board/common/post-image.sh

@@ -10,6 +10,7 @@ signkey=$3
 
 $common/sign.sh $arch $signkey
 $common/mkfit.sh
+$common/mkmmc.sh
 
 if [ "$BR2_ARCH" = "x86_64" ]; then
 	"$common/mkgns3a.sh"