intel: Add a macro for printing a debug warning once.

intel: Add a macro for printing a debug warning once.

There are a number of places where some obscure piece of the code is not
currently worth fixing, and we have some workaround behavior available.  It's
nicer for users to do some lame workaround than to just assert, but without
asserts we never knew when the workaround was at fault.

This should give us a nice compromise: Execute the workaround, but mention
that the obscure workaround was hit.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>