pru: Add initial pru_rpmsg library code for Beaglebone PRU

Add external code for using RPMsg on the Beaglebone PRU.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

lib/pru_rpmsg/pru_rpmsg.patch

@@ -0,0 +1,16 @@
+diff --git a/lib/pru_rpmsg/include/am335x/pru_iep.h b/lib/pru_rpmsg/include/am335x/pru_iep.h
+index d877ddd..064fb42 100644
+--- a/lib/pru_rpmsg/include/am335x/pru_iep.h
++++ b/lib/pru_rpmsg/include/am335x/pru_iep.h
+@@ -251,6 +251,11 @@ typedef struct {
+ 
+ } pruIep;
+ 
++#ifdef __GNUC__
++static volatile pruIntc *__CT_IEP = (void *)0x0002e000;
++#define CT_IEP	(*__CT_INTC)
++#else
+ volatile __far pruIep CT_IEP __attribute__((cregister("PRU_IEP", far), peripheral));
++#endif
+ 
+ #endif /* _PRU_IEP_H_ */