translate_all: DEBUG_FLUSH -> DEBUG_TB_FLUSH

Make the debug define consistent with the others. The flush operation is
all about invalidating TranslationBlocks on flush events.

Also fix up the commenting on the other DEBUG for the benefit of
checkpatch.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Message-Id: <20161027151030.20863-3-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
