Explicitly set rbp_internal_size for TARGET_PSOC6

The default computation assumes that a flash sector is several times
larger than a flash page. On PSoC 6 targets this is not the case
(the two values are the same) so the computed size is too small.

features/storage/kvstore/conf/filesystem/mbed_lib.json

@@ -33,6 +33,10 @@
             "help": "Path for the working directory where the FileSystemStore stores the data",
             "value": "kvstore"
         }
+    },
+    "target_overrides": {
+        "MCU_PSOC6": {
+            "rbp_internal_size": 7168
+        }
     }
 }
-

features/storage/kvstore/conf/tdb_external/mbed_lib.json

@@ -1,5 +1,4 @@
 {
-
     "name": "storage_tdb_external",
     "config": {
         "rbp_internal_size": {
@@ -22,5 +21,10 @@
             "help": "The default will set start address to address 0",
             "value": "0"
         }
+    },
+    "target_overrides": {
+        "MCU_PSOC6": {
+            "rbp_internal_size": "7168"
+        }
     }
-}
+}