Xilinx FPGA SPIx4 配置速度50M约束语句（Vivado开发环境）
qspi_50m.xdc文件：
set_property BITSTREAM.GENERAL.COMPRESS TRUE [current_design]
set_property BITSTREAM.CONFIG.SPI_BUSWIDTH 4 [current_design]
set_property BITSTREAM.CONFIG.CONFIGRATE 50 [current_design]
set_property CONFIG_VOLTAGE 3.3 [current_design]
set_property CFGBVS VCCO [current_design]
等同于图形化配置方式：
