fpga: of-fpga-region: add authenticate-fpga-config property

commit e6ea5b58fbe858e0951a5d1ce68f4142232c8eec from
https://github.com/altera-opensource/linux-socfpga.git



Add authenticate-fpga-config property to support FPGA bitstream
authentication, which makes sure a signed bitstream has valid signatures.

Signed-off-by: Richard Gong <richard.gong@intel.com>
Signed-off-by: Liwei Song <liwei.song@windriver.com>