When registering a filesystem device add a device parameter suitable
for the Linux root= option to boot from exactly this filesystem. Currently
the fs layer sets this parameter to the root=PARTUUID= mechanism if a
partuuid is available. Other filesystems like NFS and UBIFS which do
not have a PARTUUID can overwrite this.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>