Co-authored-by: q66 <daniel@octaforge.org>

 - with our boot.scr this is a no-op because flash-kernel stores a
   symlink from /dtb-5.18.0-4-arm64 to /dtbs/${fk_kvers}/${fdtfile}
 - with extlinux.conf under debian-installer only sets fdtdir to /dtbs/
   and then expects u-boot to read /dtbs/freescale/imx8mq-mnt-reform2.dtb
 - without this patch, u-boot will try reading /dtbs/imx8mq-MNT Reform 2.0.dtb
   which doesn't exist

 - this partially reverts b3a8287b which prevented BOOTENV as set by
   config_distro_boot.h being appended to CONFIG_EXTRA_ENV_SETTINGS
 - distro_bootcmd can do everything the nested loop can do:
     * boot from usb
     * arbitrary boot order
     * set arbitrary boot partition
     * search arbitrary list of prefixes
     * load a boot.scr
 - in addition to that, distro_bootcmd:
     * is the standard boot mechanism for distros (see doc/README.distro)
     * thus we can replace hard-to-read custom code
     * works with extlinux.conf (needed for debian-installer)

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>