scripts: xxdi.pl: add xxd -i compat mode

scripts: xxdi.pl: add xxd -i compat mode

So it can serve as a standalone drop in replacement for xxd utility used
currently mostly in U-Boot packages with `xxd -i` mode which outputs C
include file style, with aim for byte to byte identical output, so the
eventual difference in the generated output is easily spottable.

Fixes: #10555
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Jo-Philipp Wich <jo@mein.io> [perl-fu]
(cherry picked from commit 06e01e817ec6643a35beb9e6946689e9cc7d020a)