tools: ynl: create local ARRAY_SIZE() helper

libc doesn't have an ARRAY_SIZE() create one locally.

Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Link: https://lore.kernel.org/r/20240227223032.1835527-6-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>