translate-all: notify plugin code of tb_flush

translate-all: notify plugin code of tb_flush

Plugins might allocate per-TB data that then they get passed each
time a TB is executed (via the *userdata pointer).

Notify plugin code every time a code cache flush occurs, so
that plugins can then reclaim the memory of the per-TB data.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>