Bug#783073: bootscripts: Support using fdtfile variable passed from u-boot

[Ian Campbell <ijc@hellion.org.uk>]

On Tue, 2015-04-21 at 08:54 -0700, Vagrant Cascadian wrote:
>    load ${device} ${partition} ${loadaddr} ${pathprefix}vmlinuz-${kvers} \
> -  && load ${device} ${partition} ${fdtaddr} ${pathprefix}dtb-${kvers} \
> +  && load ${device} ${partition} ${fdtaddr} ${pathprefix}dtbs-${kvers}/${fdtfile} \
> +  || load ${device} ${partition} ${fdtaddr} ${pathprefix}dtb-${kvers} \

Does the precedence of && vs || work out correctly if the file at
${pathprefix}dtbs-${kvers}/${fdtfile} isn't present?

Do you know how prevalent the hush shell is in practice? It has if,
continue and exit syntax which we might use to make the script a bit
more readable and less error prone by doing "if ! load something ; then
echo ... ; continue ... ; fi".

For the non-generic bootscr can we switch unconditionally to fdtfile on
platforms where it always exists? That would simplify things I think and
keep the complexity in the generic case only.

Ian.