bananapi,bpi-r2 description Bananapi BPI-R2 u-boot-install file-name BPI-R2-HEAD440-0k.img preserve file-name BPI-R2-HEAD1-512b.img image-offset 512 file-name preloader_iotg7623Np1_sd_1600M.bin image-offset 2048 file-name u-boot.bin image-offset 327680