wifi: rt2x00: add COMPILE_TEST

wifi: rt2x00: add COMPILE_TEST

While this driver is for a specific arch, there is nothing preventing it
from being compiled on other platforms.

Allows the various bots to test compilation and complain if a patch is
bad.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://patch.msgid.link/20250722212856.11343-2-rosenp@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>