[PATCH] add xt25f32b, which is soldered down to Rock Pi 4b

With the attached patch, plus (only) the DTSI and defconfig patch from armbian [1], mainline uboot gets at least as far as the TPL on the Rock Pi 4B booting from the soldered-down SPI flash.

[1] https://raw.githubusercontent.com/armbian/build/master/patch/u-boot/u-boot-r...