All the pieces finally came together. I made a fresh install of Ubuntu, installed all the needed tools. cloned flashrom, modified sb600spi.c per Rene's patch to include my AMD X570 "0x61" spi, did a make install, and it works!
root@clay-MS-7C37:~# flashrom -p internal flashrom v1.2-135-g07edbb9-dirty on Linux 5.8.0-26-generic (x86_64) flashrom is free software, get the source code at https://flashrom.org Using clock_gettime for delay loops (clk_id: 1, resolution: 1ns). Found chipset "AMD FP4". Enabling flash write... Warning: spireadmode not set, leaving spireadmode unchanged.Warning: spispeed not set, leaving spispeed unchanged.OK. Found Winbond flash chip "W25Q256.W" (32768 kB, SPI) mapped at physical address 0x00000000fe000000. No operations were specified. root@clay-MS-7C37:~#
Thanks to everyone, Clay (Boot_Dawg)