target/arm: Add missing M profile case to regime_is_user()

When we added the ARMMMUIdx_MSUser MMU index we forgot to
add it to the case statement in regime_is_user(), so we
weren't treating it as unprivileged when doing MPU lookups.
Correct the omission.

Backports commit 871bec7c44a453d9cab972ce1b5d12e1af0545ab from qemu

qemu/target/arm/helper.c

@@ -7206,6 +7206,7 @@ static inline bool regime_is_user(CPUARMState *env, ARMMMUIdx mmu_idx)
     case ARMMMUIdx_S1SE0:
     case ARMMMUIdx_S1NSE0:
     case ARMMMUIdx_MUser:
+    case ARMMMUIdx_MSUser:
         return true;
     default:
         return false;