target/arm: Use TRANS_FEAT for do_narrow_extract

Rename from do_sve2_narrow_extract and hoist the sve2
check into the TRANS_FEAT macro.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220527181907.189259-109-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>