target-arm: Implement ARMv8 MVFR registers

For ARMv8 there are two changes to the MVFR media feature registers:
 * there is a new MVFR2 which is accessible from 32 bit code
 * 64 bit code accesses these via the usual sysreg instructions
   rather than with a floating-point specific instruction

Implement this.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 0ce4c26..ec0306b 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -572,6 +572,7 @@
 /* VFP system registers.  */
 #define ARM_VFP_FPSID   0
 #define ARM_VFP_FPSCR   1
+#define ARM_VFP_MVFR2   5
 #define ARM_VFP_MVFR1   6
 #define ARM_VFP_MVFR0   7
 #define ARM_VFP_FPEXC   8