Platform: Add NV counter interface

This patch adds the TF-M non-volatile(NV) counter interface.

Change-Id: I2b87dfadf9c53bd755f26867de678a4e837bbdcb
Signed-off-by: Marc Moreno <marc.morenoberengue@arm.com>
diff --git a/platform/include/tfm_plat_defs.h b/platform/include/tfm_plat_defs.h
index 308b002..5b6d169 100644
--- a/platform/include/tfm_plat_defs.h
+++ b/platform/include/tfm_plat_defs.h
@@ -18,6 +18,7 @@
 enum tfm_plat_err_t {
     TFM_PLAT_ERR_SUCCESS = 0,
     TFM_PLAT_ERR_SYSTEM_ERR,
+    TFM_PLAT_ERR_MAX_VALUE,
     /* Following entry is only to ensure the error code of int size */
     TFM_PLAT_ERR_FORCE_INT_SIZE = INT_MAX
 };