To ease TLB debugging add a few trace events, which are disabled
by default so that there's no performance impact.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Message-Id: <20190311191602.25796-5-svens@stackframe.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>