target-arm: Convert MPIDR

Convert the MPIDR to the new cp15 register scheme.
This includes giving it its own feature bit rather
than doing a CPUID value check.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 0b984d8..2630fe7 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -386,6 +386,7 @@
     ARM_FEATURE_CACHE_TEST_CLEAN, /* 926/1026 style test-and-clean ops */
     ARM_FEATURE_CACHE_DIRTY_REG, /* 1136/1176 cache dirty status register */
     ARM_FEATURE_CACHE_BLOCK_OPS, /* v6 optional cache block operations */
+    ARM_FEATURE_MPIDR, /* has cp15 MPIDR */
 };
 
 static inline int arm_feature(CPUARMState *env, int feature)