arm: Don't clear ARM_FEATURE_PMSA for no-mpu configs

Fix the handling of QOM properties for PMSA CPUs with no MPU:

Allow no-MPU to be specified by either:
 * has-mpu = false
 * pmsav7_dregion = 0
and make setting one imply the other. Don't clear the PMSA
feature bit in this situation.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 1493122030-32191-6-git-send-email-peter.maydell@linaro.org

target/arm/cpu.c

@@ -763,8 +763,14 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         cpu->id_pfr1 &= ~0xf000;
     }
 
+    /* MPU can be configured out of a PMSA CPU either by setting has-mpu
+     * to false or by setting pmsav7-dregion to 0.
+     */
     if (!cpu->has_mpu) {
-        unset_feature(env, ARM_FEATURE_PMSA);
+        cpu->pmsav7_dregion = 0;
+    }
+    if (cpu->pmsav7_dregion == 0) {
+        cpu->has_mpu = false;
     }
 
     if (arm_feature(env, ARM_FEATURE_PMSA) &&