fpga: add FPGA DFL PCIe device driver

This patch implements the basic framework of the driver for FPGA PCIe
device which implements the Device Feature List (DFL) in its MMIO space.
This driver is verified on Intel(R) PCIe-based FPGA DFL devices, including
both integrated (e.g. Intel Server Platform with In-package FPGA) and
discrete (e.g. Intel FPGA PCIe Acceleration Cards) solutions.

Signed-off-by: Tim Whisonant <tim.whisonant@intel.com>
Signed-off-by: Enno Luebbers <enno.luebbers@intel.com>
Signed-off-by: Shiva Rao <shiva.rao@intel.com>
Signed-off-by: Christopher Rauer <christopher.rauer@intel.com>
Signed-off-by: Zhang Yi <yi.z.zhang@intel.com>
Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Alan Tull <atull@kernel.org>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>