x86: include kmod-fs-vfat by default in generic images
As x86/64 and x86/generic may be using UEFI, mounting the FAT-32 /boot
is necessary in order not to loose configuration files accross
sysupgrades. Include kmod-fs-vfat by default to make sure /boot can
always be mounted.
Signed-off-by: Daniel Golle <[email protected]>