[test][hwreg] Relocate unit tests to exist alongside source

Change-Id: Ia3851cab38e65b8d7be572aba9c5b89dc92c8167

zircon/system/utest/libhwreg/BUILD.gn → zircon/system/ulib/hwreg/test/BUILD.gn

@@ -2,6 +2,13 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+group("test") {
+  testonly = true
+  deps = [
+    ":libhwreg",
+  ]
+}
+
 test("libhwreg") {
   sources = [
     "bitfields-test.cpp",

zircon/system/utest/BUILD.gn

@@ -76,6 +76,7 @@ if (current_cpu != "") {
       "$zx/system/ulib/fvm/test",
       "$zx/system/ulib/fzl/test",
       "$zx/system/ulib/gpt/test",
+      "$zx/system/ulib/hwreg/test",
       "$zx/system/ulib/id_allocator/test",
       "$zx/system/ulib/launchpad/test",
       "$zx/system/ulib/libzbi/test",
@@ -148,7 +149,6 @@ if (current_cpu != "") {
       "int-types",
       "kcounter",
       "kernel-unittests",
-      "libhwreg",
       "log",
       "logger",
       "memfs",