udmabuf: add MEMFD_CREATE dependency

udmabuf builds without it, but if userspace can not create memfd
handles in the first place it is rather pointless to include it,
except for test builds.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20180911134216.9760-7-kraxel@redhat.com

drivers/dma-buf/Kconfig

@@ -34,6 +34,7 @@ config UDMABUF
 	bool "userspace dmabuf misc driver"
 	default n
 	depends on DMA_SHARED_BUFFER
+	depends on MEMFD_CREATE || COMPILE_TEST
 	help
 	  A driver to let userspace turn memfd regions into dma-bufs.
 	  Qemu can use this to create host dmabufs for guest framebuffers.