V4L/DVB (9227): MFE: Add multi-frontend mutual exclusion

This add frontend R/W mutual exclusion.
Prior to this point in time it was possible to open both
frontends simultaneously which an MFE card cannot support.

In order to stop this, a delayed open is performed which
has the following function:

-  Return EBUSY after a configurable amount of time
   if a frontend is unavailable due to the other being
   in use.

-  Only allow opening of a frontend if the kernel thread
   of the other has stopped.

This solution was chosen to allow switching between
frontends to work as seamlessly as possible. When both
frontends are actually opened simultaneously then one
will only open, but if quick switching is performed
between one of many then the new open will succeed in
a clean fashion rather than interrupting a kernel
thread.

Signed-off-by: Darron Broad <darron@kewl.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/media/videobuf-dvb.h

@@ -43,7 +43,8 @@ int videobuf_dvb_register_bus(struct videobuf_dvb_frontends *f,
 			  struct module *module,
 			  void *adapter_priv,
 			  struct device *device,
-			  short *adapter_nr);   //NEW
+			  short *adapter_nr,
+			  int mfe_shared);
 
 void videobuf_dvb_unregister_bus(struct videobuf_dvb_frontends *f);
 
@@ -52,7 +53,8 @@ int videobuf_dvb_register_adapter(struct videobuf_dvb_frontends *f,
 			  void *adapter_priv,
 			  struct device *device,
 			  char *adapter_name,
-			  short *adapter_nr);   //NEW
+			  short *adapter_nr,
+			  int mfe_shared);
 
 int videobuf_dvb_register_frontend(struct dvb_adapter *adapter, struct videobuf_dvb *dvb);