Moved load_driver() and load_driver_symbols() over to devfs.

Added new devfs_add_driver() function that the device manager will now call
to register new drivers.
Devfs will now keep a list of known drivers and remembers, if they have
been initialized already - a driver can now safely scan the directory it's
in while being scanned itself without having its hooks called twice.
Devfs is now using a recursive lock instead of a mutex (that's not really
a requirement right now, but would allow us to keep the fs lock during
scanning).


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12933 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/fs/devfs.h

@@ -16,6 +16,8 @@
 extern "C" {
 #endif
 
+status_t devfs_add_driver(const char *path);
+
 status_t devfs_unpublish_file_device(const char *path);
 status_t devfs_publish_file_device(const char *path, const char *filePath);