recovery: Split main() into recovery_main.cpp.

This prepares for moving more codes from recovery into librecovery, so
that they will become more easily testable. recovery_main.cpp will be
the source code for recovery module, with the rest moved into
librecovery. recovery_main.cpp mainly does the initializations, such as
setting up the logger.

Test: mmma -j bootable/recovery
Test: recovery_component_test
Test: Build and boot into recovery image on marlin.
Change-Id: I8e846524546b6f3f0e32ed869e851f62261eef23
(cherry picked from commit c241cb662440551eb0d2f42345f7ee08cf60a7dd)
diff --git a/private/recovery.h b/private/recovery.h
new file mode 100644
index 0000000..5b2ca4b
--- /dev/null
+++ b/private/recovery.h
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+int start_recovery(int argc, char** argv);