image.bbclass: default USE_DEVFS to '1'

image.bbclass: default USE_DEVFS to '1'

Default USE_DEVFS to "1" so that the `makedevs' command is not run
at rootfs time by default. There are mainly two reasons to do so.

1. This will fix a build failure with initramfs-kexecboot-klibc-image.
   "makedevs: No entry for root in search list "

2. Most of our images use a filesystem over /dev. Most of the time, it's
   just devtmpfs. So we actually are using a filesystem over /dev.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>