gemini: only provide squashfs image for storlink-derivates

The itian sq201, raidsonic ib-4220-b and storlink sl93512r
can't boot from ext4. This is because the rootfstype in the
device-tree bootargs is set to "squashfs,jffs2". (And ext4
was not designed for raw NOR flash chips).

Signed-off-by: Christian Lamparter <[email protected]>

target/linux/gemini/image/Makefile

@@ -181,6 +181,7 @@ define Device/storlink-reference
 	COMPILE := copy-kernel-$(1).bin
 	COMPILE/copy-kernel-$(1).bin := copy-kernel.bin
 	IMAGES := factory.bin
+	FILESYSTEMS := squashfs
 	IMAGE/factory.bin := append-rootfs | pad-rootfs | pad-to 6144k | \
 		storlink-default-images $(1)
 	DEVICE_PACKAGES := $(GEMINI_NAS_PACKAGES)