cboot: update version string generation
cboot: update version string generation

Make the version string a variable so it can be overridden
if needed, and use a default format that includes the full
L4T version number plus ${TARGET_VENDOR}.

Exclude the build date to make these builds more
reproducibility-friendly.

Signed-off-by: Matt Madison <1fa2ef4755a9226cb9a0a4840bd89b158ac71391@madison.systems>

madisongh/meta-tegra,madisongh/meta-tegra,madisongh/meta-tegra,madisongh/meta-tegra,madisongh/meta-tegra