v4l2-pci-skeleton: Only build if PCI is available

Currently arm64 does not support PCI but it does support v4l2. Since the
PCI skeleton driver is built unconditionally as a module with no dependency
on PCI this causes build failures for arm64 allmodconfig. Fix this by
defining a symbol VIDEO_PCI_SKELETON for the skeleton and conditionalising
the build on that.

Signed-off-by: Mark Brown <[e-mail]>
Signed-off-by: Randy Dunlap <[e-mail]> [added VIDEO dependencies]
Signed-off-by: Jiri Kosina <[e-mail]>

Documentation/video4linux/Makefile

···
-obj-m := v4l2-pci-skeleton.o
+obj-$(CONFIG_VIDEO_PCI_SKELETON) := v4l2-pci-skeleton.o

drivers/media/v4l2-core/Kconfig

···
 
 	  When in doubt, say N.
 
+config VIDEO_PCI_SKELETON
+	tristate "Skeleton PCI V4L2 driver"
+	depends on PCI && BUILD_DOCSRC
+	depends on VIDEO_V4L2 && VIDEOBUF2_CORE
+	depends on VIDEOBUF2_MEMOPS && VIDEOBUF2_DMA_CONTIG
+	---help---
+	  Enable build of the skeleton PCI driver, used as a reference
+	  when developing new drivers.
+
 # Used by drivers that need tuner.ko
 config VIDEO_TUNER
 	tristate