vfio-mdev: add back CONFIG_VFIO dependency

CONFIG_VFIO_MDEV cannot be selected when VFIO itself is
disabled, otherwise we get a link failure:

WARNING: unmet direct dependencies detected for VFIO_MDEV
  Depends on [n]: VFIO [=n]
  Selected by [y]:
  - SAMPLE_VFIO_MDEV_MTTY [=y] && SAMPLES [=y]
  - SAMPLE_VFIO_MDEV_MDPY [=y] && SAMPLES [=y]
  - SAMPLE_VFIO_MDEV_MBOCHS [=y] && SAMPLES [=y]
/home/arnd/cross/arm64/gcc-13.0.1-nolibc/x86_64-linux/bin/x86_64-linux-ld: samples/vfio-mdev/mdpy.o: in function `mdpy_remove':
mdpy.c:(.text+0x1e1): undefined reference to `vfio_unregister_group_dev'
/home/arnd/cross/arm64/gcc-13.0.1-nolibc/x86_64-linux/bin/x86_64-linux-ld: samples/vfio-mdev/mdpy.o: in function `mdpy_probe':
mdpy.c:(.text+0x149e): undefined reference to `_vfio_alloc_device'

Fixes: 8bf8c5ee ("vfio-mdev: turn VFIO_MDEV into a selectable symbol")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230126211211.1762319-1-arnd@kernel.orgSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

arch/s390/Kconfig

@@ -714,6 +714,7 @@ config VFIO_CCW
 	def_tristate n
 	prompt "Support for VFIO-CCW subchannels"
 	depends on S390_CCW_IOMMU
+	depends on VFIO
 	select VFIO_MDEV
 	help
 	  This driver allows usage of I/O subchannels via VFIO-CCW.
@@ -725,8 +726,9 @@ config VFIO_AP
 	def_tristate n
 	prompt "VFIO support for AP devices"
 	depends on S390_AP_IOMMU && KVM
-	select VFIO_MDEV
+	depends on VFIO
 	depends on ZCRYPT
+	select VFIO_MDEV
 	help
 	  This driver grants access to Adjunct Processor (AP) devices
 	  via the VFIO mediated device interface.

drivers/gpu/drm/i915/Kconfig

@@ -116,6 +116,7 @@ config DRM_I915_GVT_KVMGT
 	depends on X86
 	depends on 64BIT
 	depends on KVM
+	depends on VFIO
 	select DRM_I915_GVT
 	select KVM_EXTERNAL_WRITE_TRACKING
 	select VFIO_MDEV

samples/Kconfig

@@ -185,6 +185,7 @@ config SAMPLE_UHID
 
 config SAMPLE_VFIO_MDEV_MTTY
 	tristate "Build VFIO mtty example mediated device sample code"
+	depends on VFIO
 	select VFIO_MDEV
 	help
 	  Build a virtual tty sample driver for use as a VFIO
@@ -192,6 +193,7 @@ config SAMPLE_VFIO_MDEV_MTTY
 
 config SAMPLE_VFIO_MDEV_MDPY
 	tristate "Build VFIO mdpy example mediated device sample code"
+	depends on VFIO
 	select VFIO_MDEV
 	help
 	  Build a virtual display sample driver for use as a VFIO
@@ -209,6 +211,7 @@ config SAMPLE_VFIO_MDEV_MDPY_FB
 
 config SAMPLE_VFIO_MDEV_MBOCHS
 	tristate "Build VFIO mdpy example mediated device sample code"
+	depends on VFIO
 	select VFIO_MDEV
 	select DMA_SHARED_BUFFER
 	help