Platform: Add new NV counter for supported targets

Add new NV counter to the NV counter flash area to be used
by the bootloader as a security counter.

Change-Id: I40b62b35f62d2c2c92724549ebfc58814263652e
Signed-off-by: David Vincze <david.vincze@arm.com>
diff --git a/platform/include/tfm_plat_nv_counters.h b/platform/include/tfm_plat_nv_counters.h
index 26e213b..d79c235 100644
--- a/platform/include/tfm_plat_nv_counters.h
+++ b/platform/include/tfm_plat_nv_counters.h
@@ -22,6 +22,8 @@
     PLAT_NV_COUNTER_0 = 0,  /* Used by SST service */
     PLAT_NV_COUNTER_1,      /* Used by SST service */
     PLAT_NV_COUNTER_2,      /* Used by SST service */
+    PLAT_NV_COUNTER_3,      /* Used by bootloader */
+    PLAT_NV_COUNTER_MAX
 };
 
 #ifdef __cplusplus