Platform: Add new NV counter due to multiple image boot

Add new NV counter to the NV counter flash area to be used
by the bootloader as a separate second security counter
for another firmware image to enable multiple image boot.

Change-Id: I6cd3bf675317240e40cd0bc31a714070885791aa
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 9b86112..ff34a91 100644
--- a/platform/include/tfm_plat_nv_counters.h
+++ b/platform/include/tfm_plat_nv_counters.h
@@ -31,6 +31,7 @@
     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_4,      /* Used by bootloader */
     PLAT_NV_COUNTER_MAX
 };