Copying debug ramdisk files to /debug_ramdisk/*

In previous implementation, userdebug sepoilcy and property files are
loaded from the system.img. This CL changes this to:

  - first-stage init copies userdebug files from ramdisk to /debug_ramisk/*
  - second-stage init loads files from /debug_ramdisk/*.

Note: same as before, the above can only be triggered, if the device
is UNLOCKED

With this, we don't have to put userdebug related files into the USER
system.img.

Bug: 126493225
Test: boot device with a ramdisk with /force_debuggable, checks related
      files are loaded
Change-Id: I63f5f846e82ba78427062bf7615c26173878d8f3
diff --git a/init/init.cpp b/init/init.cpp
index 0f44efd..82415f9 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -621,6 +621,12 @@
     });
 }
 
+static void UmountDebugRamdisk() {
+    if (umount("/debug_ramdisk") != 0) {
+        LOG(ERROR) << "Failed to umount /debug_ramdisk";
+    }
+}
+
 int SecondStageMain(int argc, char** argv) {
     if (REBOOT_BOOTLOADER_ON_PANIC) {
         InstallRebootSignalHandlers();
@@ -685,6 +691,7 @@
     InstallSignalFdHandler(&epoll);
 
     property_load_boot_defaults(load_debug_prop);
+    UmountDebugRamdisk();
     fs_mgr_vendor_overlay_mount_all();
     export_oem_lock_status();
     StartPropertyService(&epoll);