greybus: kernel_ver.h: add sysfs_create_groups() and sysfs_remove_groups()

These functions showed up in 3.12 or so, and we are stuck on 3.10 for
various reasons, so provide backports in kernel_ver.h so that we can
rely on these functions.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>