fpga: dfl: fme: add header sub feature support

The Header Register set is always present for FPGA Management Engine (FME),
this patch implements init and uinit function for header sub feature and
introduces several read-only sysfs interfaces for the capability and
status.

Sysfs interfaces:
* /sys/class/fpga_region/<regionX>/<dfl-fme.x>/ports_num
  Read-only. Number of ports implemented

* /sys/class/fpga_region/<regionX>/<dfl-fme.x>/bitstream_id
  Read-only. Bitstream (static FPGA region) identifier number. It contains
  the detailed version and other information of this static FPGA region.

* /sys/class/fpga_region/<regionX>/<dfl-fme.x>/bitstream_metadata
  Read-only. Bitstream (static FPGA region) meta data. It contains the
  synthesis date, seed and other information of this static FPGA region.

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: Kang Luwei <luwei.kang@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>