target/arm: Convert BR, BLR, RET to decodetree

Convert the simple (non-pointer-auth) BR, BLR and RET insns
to decodetree.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230512144106.3608981-18-peter.maydell@linaro.org
2 files changed