RockPi4: patch to add XTX (Shenzhen Xin Tian Xia Tech) SPI flash
As RockPi 4B comes with such SPI flash soldered in factory, there is a need to add support for it into kernel.
There will be support for xt25f32b and xt25f128b chips. This chips allow u-booting from various sources – NVMe, eMMC, USB. One just need to flash them with correct u-boot. This patch allows for it (together with DTBO).
This patch comes from Armbian and it is being used there for a quite some time - Jun 2020.
I have tested it on 5.10.10-1-MANJARO-ARM to find it working ok.