target/arm: Implement MVE VADC, VSBC

target/arm: Implement MVE VADC, VSBC

Implement the MVE VADC and VSBC insns.  These perform an
add-with-carry or subtract-with-carry of the 32-bit elements in each
lane of the input vectors, where the carry-out of each add is the
carry-in of the next.  The initial carry input is either 1 or is from
FPSCR.C; the carry out at the end is written back to FPSCR.C.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210617121628.20116-41-peter.maydell@linaro.org