kbuild: Support a FIT_EXTRA_ARGS environment variable

kbuild: Support a FIT_EXTRA_ARGS environment variable

In some cases it is useful to be able to pass additional flags to the
make_fit.py script. For example, since ramdisks are typically large,
passing -E to use external data can be helpful.

Add a new FIT_EXTRA_ARGS variable for this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/20260106162738.2605574-5-sjg@chromium.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>