Use proper mkfs.ext4 when creating /var and /cfg partitions

Without this it used an genimage internal one, which did not set
the filetype feature on the filesystem. This caused
podman to refuse to start

board/common/genimage.cfg

@@ -1,65 +0,0 @@
-
-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.squashfs"
-		size = 224M
-	}
-
-	partition secondary {
-		bootable = true
-		image = "rootfs.squashfs"
-		size = 224M
-	}
-
-	partition cfg {
-		image = "cfg.ext4"
-	}
-
-	partition var {
-		image = "var.ext4"
-	}
-}
-
-# Silence genimage warnings
-config {}

board/common/genimage.cfg.in

@@ -7,6 +7,7 @@ image aux.ext4 {
 
 	ext4 {
 		label = "aux"
+		use-mke2fs = true
 	}
 }
 
@@ -17,6 +18,7 @@ image cfg.ext4 {
 
 	ext4 {
 		label = "cfg"
+		use-mke2fs = true
 	}
 }
 
@@ -27,6 +29,7 @@ image var.ext4 {
 
 	ext4 {
 		label = "var"
+		use-mke2fs = true
 	}
 }