powerpc: Restore VDSO information on critical exception om BookE

Critical exception on 64-bit booke uses user-visible SPRG3 as scratch.
Restore VDSO information in SPRG3 on exception prolog.

Use a common sprg3 field in PACA for all powerpc64 architectures.

Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index 7476b0a..87a82fb 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -110,7 +110,9 @@
 
 #define PROLOG_STORE_RESTORE_SCRATCH_CRIT				    \
 	mfspr	r10,SPRN_SPRG_CRIT_SCRATCH;	/* get r13 */		    \
-	std	r10,PACA_EXCRIT+EX_R13(r13)
+	std	r10,PACA_EXCRIT+EX_R13(r13);				    \
+	ld	r11,PACA_SPRG3(r13);					    \
+	mtspr	SPRN_SPRG_CRIT_SCRATCH,r11;
 
 /* Variants of the "addition" argument for the prolog
  */