For this platform the bootable artifact is imx-boot based, so configure
some variables accordingly.
Signed-off-by: Javier Viguera <javier.viguera@digi.com>
Rework the "build_uboot_scripts" to prevent changing the templates in
the WORKDIR, as those are part of the SRC_URI. Instead, change the
deployed scripts by using "sed" and redirection.
Also, removed UBOOT_HAS_FASTBOOT altogether, as there is no platform
that does not support fastboot.
Signed-off-by: Javier Viguera <javier.viguera@digi.com>