tools: ynl: decode enums in auto-ints

Use enum decoding on auto-ints. Looks like we only had enum
auto-ints for input values until now. Upcoming RSS work will
need this to declare an attribute with flags as a uint.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250708220640.2738464-3-kuba@kernel.org


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