lame: also disable debug handling on xtensa

Similar to the other architectures we have disabled it for. At the same time
also adjust the comment as we now do this for several other architectures.

Fixes http://autobuild.buildroot.net/results/b7e/b7e466580561e32fb584399e5914cd61a37bf7e9/



Signed-off-by: Peter Korsgaard <peter@korsgaard.com>