fpga manager: xilinx-spi: valid for the 7 Series too

The Xilinx 7-series uses the same protocol, mention that.
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

drivers/fpga/xilinx-spi.c

 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * Xilinx Spartan6 Slave Serial SPI Driver
+ * Xilinx Spartan6 and 7 Series Slave Serial SPI Driver
  *
  * Copyright (C) 2017 DENX Software Engineering
  *