target/arm: Fix MVE VSLI by 0 and VSRI by <dt>

target/arm: Fix MVE VSLI by 0 and VSRI by <dt>

In the MVE shift-and-insert insns, we special case VSLI by 0
and VSRI by <dt>. VSRI by <dt> means "don't update the destination",
which is what we've implemented. However VSLI by 0 is "set
destination to the input", so we don't want to use the same
special-casing that we do for VSRI by <dt>.

Since the generic logic gives the right answer for a shift
by 0, just use that.

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