target/arm: migrate system/cp trap syndromes to registerfields

Migrate syn_aa64_sysregtrap and co-processor register trap syndromes
to the registerfields API. The co-processor syndromes are split
between single and duel register moves.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20260422125250.1303100-3-alex.bennee@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>