scripts: add script to extract built-in firmware blobs

scripts: add script to extract built-in firmware blobs

There is currently no tool to extract a firmware blob that is built-in
on vmlinux to the best of my knowledge.  So if we have a kernel image
containing the blobs, and we want to rebuild the kernel with some debug
patches for example (and given that the image also has IKCONFIG=y), we
currently can't do that for the same versions for all the firmware
blobs, _unless_ we have exact commits of linux-firmware for the
specific versions for each firmware included.

Through the options CONFIG_EXTRA_FIRMWARE{_DIR} one is able to build a
kernel including firmware blobs in a built-in fashion.  This is usually
the case of built-in drivers that require some blobs in order to work
properly, for example, like in non-initrd based systems.

Add hereby a script to extract these blobs from a non-stripped vmlinux,
similar to the idea of "extract-ikconfig".  The firmware loader interface
saves such built-in blobs as rodata entries, having a field for the FW
name as "_fw_<module_name>_<firmware_name>_bin"; the tool extracts files
named "<module_name>_<firmware_name>" for each rodata firmware entry
detected.  It makes use of awk, bash, dd and readelf, pretty standard
tooling for Linux development.

With this tool, we can blindly extract the FWs and easily re-add them
in the new debug kernel build, allowing a more deterministic testing
without the burden of "hunting down" the proper version of each
firmware binary.

Link: https://lkml.kernel.org/r/20250120190436.127578-1-gpiccoli@igalia.com
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Suggested-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Reviewed-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Luis Chamberalin <mcgrof@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Russ Weight <russ.weight@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>