Driver mapping refactory.

VFS CHANGES:
- dmap table no longer statically initialized in VFS
- Dropped FSSIGNON svrctl call no longer used by INET

INET CHANGES:
- INET announces its presence to VFS just like any other driver

RS CHANGES:
- The boot image dev table contains all the data to initialize VFS' dmap table
- RS interface supports asynchronous up and update operations now
- RS interface extended to support driver style and flags

servers/vfs/dmap.h

@@ -11,14 +11,13 @@ dmap.h
  * The table can be update dynamically. The field 'dmap_flags' describe an 
  * entry's current status and determines what control options are possible. 
  */
-#define DMAP_MUTABLE		0x01	/* mapping can be overtaken */
 
 extern struct dmap {
   int _PROTOTYPE ((*dmap_opcl), (int, Dev_t, int, int) );
   int _PROTOTYPE ((*dmap_io), (int, message *) );
   endpoint_t dmap_driver;
-  int dmap_flags;
   char dmap_label[LABEL_MAX];
-  int dmap_async_driver;
+  int dmap_flags;
+  int dmap_style;
   struct filp *dmap_sel_filp;
 } dmap[];