framebuffer not working with dtoverlay=vc4-fkms-v3d on RPi3 aarch64.

On Raspberry Pi 3 B Plus with kernel 5.6.16-rpi-un-alt1 occurs
framebuffer error with dtoverlay=vc4-kms-v3d (antohami@)

- Return 0 at the end of the script

Also added download support on the Raspberry Pi 3.
The following feature has appeared. The FAT partition does not
install the last installed kernel, but the first kernel in the
KFLAVOURS list. This was done in order to enable  u-boot to
default load another kernel, for example std-def.

The feature фкь-кзш4 is available for armh now.

command "rpi4-boot-nouboot --bootstrap" creates
files of kernel, initrd, dtb, cmdline.txt, config.txt
in /usr/share/u-boot/rpi_4