powerpc/booke64: Use GSRR registers in Guest Doorbell interrupts

Guest Doorbell interrupts use guest save and restore registers. Add a new
Guest Doorbell exception type to accommodate GSRR0/1 SPRs usage in exception
prolog and fix the exception handler.

Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/exception-64e.h b/arch/powerpc/include/asm/exception-64e.h
index ac13add..e73452f 100644
--- a/arch/powerpc/include/asm/exception-64e.h
+++ b/arch/powerpc/include/asm/exception-64e.h
@@ -37,6 +37,7 @@
  * critical data
  */
 
+#define PACA_EXGDBELL PACA_EXGEN
 
 /* We are out of SPRGs so we save some things in the PACA. The normal
  * exception frame is smaller than the CRIT or MC one though
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 43bb15f..c195bf0 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -863,6 +863,7 @@
 #define SPRN_SPRG_TLB_EXFRAME	SPRN_SPRG2
 #define SPRN_SPRG_TLB_SCRATCH	SPRN_SPRG6
 #define SPRN_SPRG_GEN_SCRATCH	SPRN_SPRG0
+#define SPRN_SPRG_GDBELL_SCRATCH SPRN_SPRG_GEN_SCRATCH
 
 #define SET_PACA(rX)	mtspr	SPRN_SPRG_PACA,rX
 #define GET_PACA(rX)	mfspr	rX,SPRN_SPRG_PACA