pw_log_basic: split bazel target

Separate headers and sources into separate targets for bazel for
pw_log_basic. This should allow Pigweed to pass stricter dependency
checks than bazel has.

Bug: 101
Change-Id: I6b60918c41b2753692aa1d48de07c1bda92041ef
diff --git a/pw_kvs/BUILD b/pw_kvs/BUILD
index e91500f..3720f93 100644
--- a/pw_kvs/BUILD
+++ b/pw_kvs/BUILD
@@ -134,6 +134,7 @@
     deps = [
         ":pw_kvs",
         ":test_utils",
+        "//pw_log:backend",
     ],
 )
 
@@ -143,6 +144,7 @@
     deps = [
         ":pw_kvs",
         ":test_utils",
+        "//pw_log:backend",
     ],
 )
 
@@ -153,7 +155,7 @@
         ":crc16",
         ":pw_kvs",
         ":test_utils",
-        "//pw_log",
+        "//pw_log:backend",
     ],
 )
 
@@ -166,7 +168,7 @@
         ":crc16",
         ":pw_kvs",
         ":test_utils",
-        "//pw_log",
+        "//pw_log:backend",
     ],
 )
 
@@ -179,6 +181,7 @@
         ":test_partition",
         ":test_utils",
         "//pw_checksum",
+        "//pw_log:backend",
     ],
 )
 
@@ -191,6 +194,7 @@
         ":test_partition",
         ":test_utils",
         "//pw_checksum",
+        "//pw_log:backend",
     ],
 )
 
@@ -200,6 +204,7 @@
     deps = [
         ":pw_kvs",
         ":test_utils",
+        "//pw_log:backend",
     ],
 )