The revision field may change between silicon revisions without changing
the mapping to a part. This avoids errors like:
  ERROR: Incorrect XILINX IDCODE 0x14738093, maskid 0x4600093
  NOTICE: ATF running on XCZUUNKN/EP108 v3/RTL5.1 at 0xfffe5000
on parts with a newer revision.

Reported-by: Love Kumar <love.kumar@xilinx.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Acked-by: Alistair Francis <alistair.francis@xilinx.com>
Tested-by: Love Kumar <love.kumar@xilinx.com>