ASoC: Intel: Fix build for sst-dsp.c on PPC architecture

Disable build on non X86 architectures except for compile testing. This fixes
the following build errors on PPC and adds an option for testing the build on other
architectures as suggested by Mark Brown :-

sound/soc/intel/sst-dsp.c: In function 'sst_dsp_outbox_write':
sound/soc/intel/sst-dsp.c:218:2: error: implicit declaration of function 'memcpy_toio' [-Werror=implicit-function-declaration]
  memcpy_toio(sst->mailbox.out_base, message, bytes);
  ^
sound/soc/intel/sst-dsp.c: In function 'sst_dsp_outbox_read':
sound/soc/intel/sst-dsp.c:231:2: error: implicit declaration of function 'memcpy_fromio' [-Werror=implicit-function-declaration]
  memcpy_fromio(message, sst->mailbox.out_base, bytes);
  ^
Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/intel/Kconfig

@@ -15,6 +15,7 @@ config SND_SST_MFLD_PLATFORM
 config SND_SOC_INTEL_SST
 	tristate "ASoC support for Intel(R) Smart Sound Technology"
 	select SND_SOC_INTEL_SST_ACPI if ACPI
+	depends on (X86 || COMPILE_TEST)
 	help
           This adds support for Intel(R) Smart Sound Technology (SST).
           Say Y if you have such a device

sound/soc/intel/sst-dsp.c

@@ -19,6 +19,7 @@
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
+#include <linux/io.h>
 
 #include "sst-dsp.h"
 #include "sst-dsp-priv.h"