ftpm: disable PPI emulation by default

Add the configuration variable CFG_FTPM_EMULATE_PPI, default disabled,
to control whether PPI emulation is enabled.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

ta/ftpm/fTPM.c

@@ -36,6 +36,7 @@
 
 #define STR_TRACE_USER_TA "fTPM"
 
+#include <config.h>
 #include <tee_internal_api.h>
 #include <tee_internal_api_extensions.h>
 #include <string.h>
@@ -467,6 +468,8 @@ TEE_Result TA_InvokeCommandEntryPoint(void      *sess_ctx,
         }
 
         case TA_FTPM_EMULATE_PPI: {
+            if (!IS_ENABLED(CFG_FTPM_EMULATE_PPI))
+                return TEE_ERROR_NOT_SUPPORTED;
             return fTPM_Emulate_PPI(param_types, params);
         }
 

ta/ftpm/sub.mk

@@ -1,3 +1,5 @@
+CFG_FTPM_EMULATE_PPI ?= n
+
 #
 # The fTPM needs to overwrite some of the header files used in the
 # reference implementation. The search order GCC uses is dependent on the