target/arm: Avoid splitting Zregs across lines in dump

Allow the line length to extend to 548 columns.  While annoyingly wide,
it's still less confusing than the continuations we print.  Also, the
default VL used by Linux (and max for A64FX) uses only 140 columns.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230622151201.1578522-2-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>