selftests/bpf: vm: add support for VIRTIO_FS

danobi/vmtest is going to migrate from using 9p to using virtio_fs to
mount the local rootfs: danobi/vmtest#88

BPF CI uses danobi/vmtest to run bpf selftests and will need to support
VIRTIO_FS.

This change enables new kconfigs to be able to support the upcoming
danobi/vmtest.

Tested by building a new kernel with those config and confirming it
would successfully run with 9p (currently what is used by vmtest), and
with virtio_fs (using a local build of vmtest).

  $ vmtest -k arch/x86/boot/bzImage "findmnt /"
  => bzImage
  ===> Booting
  ===> Setting up VM
  ===> Running command
  TARGET SOURCE    FSTYPE OPTIONS
  /      /dev/root 9p     rw,relatime,cache=5,access=client,msize=512000,trans=virtio
  $ /home/chantra/local/danobi-vmtest/target/debug/vmtest -k arch/x86/boot/bzImage "findmnt /"
  => bzImage
  ===> Initializing host environment
  ===> Booting
  ===> Setting up VM
  ===> Running command
  TARGET SOURCE FSTYPE   OPTIONS
  /      rootfs virtiofs rw,relatime

Changes in v2:
* Sorted configs alphabetically

Signed-off-by: Manu Bretelle <chantr4@gmail.com>
Acked-by: Daniel Xu <dxu@dxuuu.xyz>

Author: chantra

tools/testing/selftests/bpf/config.vm

@@ -1,12 +1,15 @@
-CONFIG_9P_FS=y
 CONFIG_9P_FS_POSIX_ACL=y
 CONFIG_9P_FS_SECURITY=y
+CONFIG_9P_FS=y
 CONFIG_CRYPTO_DEV_VIRTIO=y
-CONFIG_NET_9P=y
+CONFIG_FUSE_FS=y
+CONFIG_FUSE_PASSTHROUGH=y
 CONFIG_NET_9P_VIRTIO=y
+CONFIG_NET_9P=y
 CONFIG_VIRTIO_BALLOON=y
 CONFIG_VIRTIO_BLK=y
 CONFIG_VIRTIO_CONSOLE=y
+CONFIG_VIRTIO_FS=y
 CONFIG_VIRTIO_NET=y
 CONFIG_VIRTIO_PCI=y
 CONFIG_VIRTIO_VSOCKETS_COMMON=y