target/arm: Allow M-profile CPUs to disable the DSP extension via CPU property

Allow the DSP extension to be disabled via a CPU property for
M-profile CPUs. (A and R-profile CPUs don't have this extension
as a defined separate optional architecture extension, so
they don't need the property.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20190517174046.11146-3-peter.maydell@linaro.org

target/arm/cpu.h

@@ -790,6 +790,8 @@ struct ARMCPU {
     bool has_vfp;
     /* CPU has Neon */
     bool has_neon;
+    /* CPU has M-profile DSP extension */
+    bool has_dsp;
 
     /* CPU has memory protection unit */
     bool has_mpu;