fpga: dfl: fme: convert platform_driver to use dev_groups

This patch takes advantage of driver core which helps to create
and remove sysfs attribute files, so there is no need to register
sysfs entries manually in dfl-fme platform river code.

Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Moritz Fischer <mdf@kernel.org>