media: platform: amphion: Fix build error without MAILBOX

while COMPILE_TEST is y and MAILBOX is n, build fails:

ERROR: modpost: "mbox_request_channel_byname" [drivers/media/platform/amphion/amphion-vpu.ko] undefined!
ERROR: modpost: "mbox_free_channel" [drivers/media/platform/amphion/amphion-vpu.ko] undefined!
ERROR: modpost: "mbox_send_message" [drivers/media/platform/amphion/amphion-vpu.ko] undefined!

Adding a MAILBOX dependency in VIDEO_AMPHION_VPU to fix this.

Link: https://lore.kernel.org/linux-media/20220318030305.39120-1-yuehaibing@huawei.com
Fixes: 52b3a219 ("media: platform: amphion: move config to its own file")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/amphion/Kconfig

@@ -7,7 +7,7 @@ config VIDEO_AMPHION_VPU
 	depends on V4L_MEM2MEM_DRIVERS
 	depends on ARCH_MXC || COMPILE_TEST
 	depends on MEDIA_SUPPORT
-	depends on VIDEO_DEV
+	depends on VIDEO_DEV && MAILBOX
 	select MEDIA_CONTROLLER
 	select V4L2_MEM2MEM_DEV
 	select VIDEOBUF2_DMA_CONTIG