target/arm: Reorganize SVE WHILE

target/arm: Reorganize SVE WHILE

The pseudocode for this operation is an increment + compare loop,
so comparing <= the maximum integer produces an all-true predicate.

Rather than bound in both the inline code and the helper, pass the
helper the number of predicate bits to set instead of the number
of predicate elements to set.

Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Message-id: 20180801123111.3595-4-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit bbd0968c458d48e34a08b8694fa3309a9fe1c9e7)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>