ppc4xx: Fix dflush() to restore DVLIM register

Signed-off-by: Larry Johnson <lrj@acm.org>
diff --git a/cpu/ppc4xx/start.S b/cpu/ppc4xx/start.S
index a730604..77c2aa4 100644
--- a/cpu/ppc4xx/start.S
+++ b/cpu/ppc4xx/start.S
@@ -1700,6 +1700,7 @@
 	rlwinm	r8,r9,0,15,13
 	rlwinm	r8,r8,0,17,15
 	mtmsr	r8
+	mfspr	r8,dvlim
 	addi	r3,r0,0x0000
 	mtspr	dvlim,r3
 	mfspr	r3,ivpr
@@ -1714,6 +1715,7 @@
 ..ag:	dcbf	r0,r3
 	addi	r3,r3,-32
 	bdnz	..ag
+	mtspr	dvlim,r8
 	sync
 	mtmsr	r9
 	blr