fpga: dfl: use driver core functions, not sysfs ones.

This is a driver, do not call "raw" sysfs functions, instead call driver
core ones.  Specifically convert the use of sysfs_create_files() and
sysfs_remove_files() to use device_add_groups() and
device_remove_groups()

Cc: Wu Hao <hao.wu@intel.com>
Cc: Alan Tull <atull@kernel.org>
Cc: Moritz Fischer <mdf@kernel.org>
Cc: linux-fpga@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20190704055645.GA15471@kroah.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>