ynl: regenerate all headers

Also add support to pass topdir to ynl-regen.sh (Jakub) and call
it from the makefile to update the UAPI headers.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Co-developed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230727163001.3952878-4-sdf@google.com


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