package/libselinux: enable kernel selinux support for f2fs images

If BR2_TARGET_ROOTFS_F2FS is selected, enable the following kernel options:
  - CONFIG_F2FS_FS_XATTR
  - CONFIG_F2FS_FS_SECURITY

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>