Hexagon (target/hexagon) Move pred_written to DisasContext

The pred_written variable in the CPUHexagonState is only used for
bookkeeping within the translation of a packet.  With recent changes
that eliminate the need to free TCGv variables, these make more sense
to be transient and kept in DisasContext.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230427230012.3800327-20-tsimpson@quicinc.com>