fpga: dfl: fme: add capability sysfs interfaces

This patch adds 3 read-only sysfs interfaces for FPGA Management Engine
(FME) block for capabilities including cache_size, fabric_version and
socket_id.

Signed-off-by: Luwei Kang <luwei.kang@intel.com>
Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Alan Tull <atull@kernel.org>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Link: https://lore.kernel.org/r/1564914022-3710-11-git-send-email-hao.wu@intel.com


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