fpga: dfl: afu: add AFU state related sysfs interfaces

This patch introduces more sysfs interfaces for Accelerated
Function Unit (AFU). These interfaces allow users to read
current AFU Power State (APx), read / clear AFU Power (APx)
events which are sticky to identify transient APx state,
and manage AFU's LTR (latency tolerance reporting).

Signed-off-by: Ananda Ravuri <ananda.ravuri@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/1564914022-3710-4-git-send-email-hao.wu@intel.com


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