target-arm: Implement MDCR_EL3 and SDCR

Implement the MDCR_EL3 register (which is SDCR for AArch32).
For the moment we implement it as reads-as-written.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1454506721-11843-3-git-send-email-peter.maydell@linaro.org
diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 52284e9..cf2df50 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -382,6 +382,7 @@
         uint64_t mdscr_el1;
         uint64_t oslsr_el1; /* OS Lock Status */
         uint64_t mdcr_el2;
+        uint64_t mdcr_el3;
         /* If the counter is enabled, this stores the last time the counter
          * was reset. Otherwise it stores the counter value
          */