target/arm: Explicitly enable VFP short-vectors for aarch32 -cpu max

At the moment our -cpu max for AArch32 supports VFP short-vectors
because we always implement them, even for CPUs which should
not have them. The following commits are going to switch to
using the correct ID-register-check to enable or disable short
vector support, so we need to turn it on explicitly for -cpu max,
because Cortex-A15 doesn't implement it.

We don't enable this for the AArch64 -cpu max, because the v8A
architecture never supports short-vectors.

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

target/arm/cpu.c

@@ -2023,6 +2023,10 @@ static void arm_max_initfn(Object *obj)
         kvm_arm_set_cpu_features_from_host(cpu);
     } else {
         cortex_a15_initfn(obj);
+
+        /* old-style VFP short-vector support */
+        cpu->isar.mvfr0 = FIELD_DP32(cpu->isar.mvfr0, MVFR0, FPSHVEC, 1);
+
 #ifdef CONFIG_USER_ONLY
         /* We don't set these in system emulation mode for the moment,
          * since we don't correctly set (all of) the ID registers to