target-arm/helper.c: Allow cp15.c15 dummy override

The cp15.c15 space is implementation defined. Currently there is a
dummy placeholder register RAZing it. Allow overriding of this RAZ
so implementations of specific registers can take precedence.
Signed-off-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: ed1bacec56dae00cb398c798f8240e8e685f949c.1387160489.git.peter.crosthwaite@xilinx.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target-arm/helper.c

@@ -1338,7 +1338,8 @@ static const ARMCPRegInfo dummy_c15_cp_reginfo[] = {
      */
     { .name = "C15_IMPDEF", .cp = 15, .crn = 15,
       .crm = CP_ANY, .opc1 = CP_ANY, .opc2 = CP_ANY,
-      .access = PL1_RW, .type = ARM_CP_CONST | ARM_CP_NO_MIGRATE,
+      .access = PL1_RW,
+      .type = ARM_CP_CONST | ARM_CP_NO_MIGRATE | ARM_CP_OVERRIDE,
       .resetvalue = 0 },
     REGINFO_SENTINEL
 };