fix(cros-bootkernel/x86_64_defconfig_boot) disable some filesystems

The boot kernel does not need aufs, xfs, btrfs, or vfat, so disable them
all.
fix(cros-bootkernel/x86_64_defconfig_boot) disable ext2 and ext3

The ext4 filesystem can handle both of these types of images, so only
build it, and not the others.
fix(cros-bootkernel/x86_64_defconfig_boot) disable FUSE and PSTORE

These two options are not needed in a boot kernel.