target/arm: Speed up aarch64 TBL/TBX

target/arm: Speed up aarch64 TBL/TBX

Always perform one call instead of two for 16-byte operands.
Use byte loads/stores directly into the vector register file
instead of extractions and deposits to a 64-bit local variable.

In order to easily receive pointers into the vector register file,
convert the helper to the gvec out-of-line signature.  Move the
helper into vec_helper.c, where it can make use of H1 and clear_tail.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20210224230532.276878-1-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>