target/arm: Use isar_feature function for testing AA32HPD feature

Now we have moved ID_MMFR4 into the ARMISARegisters struct, we
can define and use an isar_feature for the presence of the
ARMv8.2-AA32HPD feature, rather than open-coding the test.

While we're here, correct a comment typo which missed an 'A'
from the feature name.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Message-id: 20200214175116.9164-20-peter.maydell@linaro.org

target/arm/cpu.h

@@ -3526,6 +3526,11 @@ static inline bool isar_feature_aa32_pmu_8_4(const ARMISARegisters *id)
         FIELD_EX32(id->id_dfr0, ID_DFR0, PERFMON) != 0xf;
 }
 
+static inline bool isar_feature_aa32_hpd(const ARMISARegisters *id)
+{
+    return FIELD_EX32(id->id_mmfr4, ID_MMFR4, HPDS) != 0;
+}
+
 /*
  * 64-bit feature tests via id registers.
  */

target/arm/helper.c

@@ -7408,8 +7408,8 @@ void register_cp_regs_for_features(ARMCPU *cpu)
     } else {
         define_arm_cp_regs(cpu, vmsa_pmsa_cp_reginfo);
         define_arm_cp_regs(cpu, vmsa_cp_reginfo);
-        /* TTCBR2 is introduced with ARMv8.2-A32HPD.  */
-        if (FIELD_EX32(cpu->isar.id_mmfr4, ID_MMFR4, HPDS) != 0) {
+        /* TTCBR2 is introduced with ARMv8.2-AA32HPD.  */
+        if (cpu_isar_feature(aa32_hpd, cpu)) {
             define_one_arm_cp_reg(cpu, &ttbcr2_reginfo);
         }
     }