pw_kvs: Fix GC selection "ping pong" bug

Fix bug in KVS GC select sector to GC that can in some cases result in
GC ping ponging between two sectors and not spreading wear across other
sectors.

The original step 1 was to search from sector 0 and select the sector
with no valid bytes and most reclaimable bytes. The search has since
been modified to start from last_new_ sector.

Now step 1 searches from last_new_ and selects the first sector with
no valid bytes and any reclaimable bytes.

Change-Id: I123c8e244b922316ccd220ee1508498540764ec9
diff --git a/pw_kvs/BUILD b/pw_kvs/BUILD
index 5a01bff..dbbddd3 100644
--- a/pw_kvs/BUILD
+++ b/pw_kvs/BUILD
@@ -241,6 +241,7 @@
     ],
     deps = [
         ":pw_kvs",
+        ":test_partition",
         ":test_utils",
         "//pw_log:backend",
         "//pw_unit_test",