Allow including initramfs-extra files in the initramfs (MR 48)

This uses a "deviceinfo_create_initfs_extra" to allow including
initramfs-extra files in the initramfs and skip creating a separate
initramfs-extra archive when it's set to "false".
If this variable is unset, mkinitfs uses a default value of "false".

internal/bootdeploy/bootdeploy.go

@@ -78,12 +78,17 @@ func (b *BootDeploy) Run() error {
 	}
 
 	// boot-deploy -i initramfs -k vmlinuz-postmarketos-rockchip -d /tmp/cpio -o /tmp/foo initramfs-extra
-	cmd := exec.Command("boot-deploy",
+	args := []string{
 		"-i", "initramfs",
 		"-k", kernFilename,
 		"-d", b.inDir,
 		"-o", b.outDir,
-		"initramfs-extra")
+	}
+
+	if b.devinfo.CreateInitfsExtra {
+		args = append(args, "initramfs-extra")
+	}
+	cmd := exec.Command("boot-deploy", args...)
 
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr