board/qemu/aarch64-virt/linux.config: enable VIRTIO_FS driver

board/qemu/aarch64-virt/linux.config: enable VIRTIO_FS driver

virtio-fs allow sharing a directory between the host and the guest.
It require virtiofsd daemon running before starting Qemu.

The wiki [1] recommand to enable the following kernel options:

      CONFIG_VIRTIO
      CONFIG_VIRTIO_FS
      CONFIG_DAX
      CONFIG_FS_DAX
      CONFIG_DAX_DRIVER
      CONFIG_ZONE_DEVICE

But virtio-fs works fine with only VIRTIO_FS.

Note: ZONE_DEVICE can only be enabled on aarch64 since kernel >= 5.7.
ARCH_ENABLE_MEMORY_HOTREMOVE support is missing for previous kernel [2].

[1] https://virtio-fs.gitlab.io/howto-qemu.html
[2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bbd6ec605c0fc286c3f8ce60b4ed44635361d58b

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>