fpga: dfl: add FPGA Accelerated Function Unit driver basic framework

On DFL FPGA devices, the Accelerated Function Unit (AFU), can be
reprogrammed for different functions. It connects to the FPGA
infrastructure (static FPGA region) via a Port. Port CSRs are
implemented separately from the AFU CSRs to provide control and
status of the Port. Once valid PR bitstream is programmed into
the AFU, it allows access to the AFU CSRs in the AFU MMIO space.

This patch only implements basic driver framework for AFU, including
device file operation framework.

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: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Alan Tull <atull@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>