powerpc/8xx: mfspr SPRN_TBRx in lieu of mftb/mftbu is not supported

Commit beb2dc0a7a84be003ce54e98b95d65cc66e6e536 breaks the MPC8xx which
seems to not support using mfspr SPRN_TBRx instead of mftb/mftbu
despite what is written in the reference manual.

This patch reverts to the use of mftb/mftbu when CONFIG_8xx is
selected.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/arch/powerpc/boot/util.S b/arch/powerpc/boot/util.S
index 5143228..6636b1d 100644
--- a/arch/powerpc/boot/util.S
+++ b/arch/powerpc/boot/util.S
@@ -71,18 +71,32 @@
 	add	r4,r4,r5
 	addi	r4,r4,-1
 	divw	r4,r4,r5	/* BUS ticks */
+#ifdef CONFIG_8xx
+1:	mftbu	r5
+	mftb	r6
+	mftbu	r7
+#else
 1:	mfspr	r5, SPRN_TBRU
 	mfspr	r6, SPRN_TBRL
 	mfspr	r7, SPRN_TBRU
+#endif
 	cmpw	0,r5,r7
 	bne	1b		/* Get [synced] base time */
 	addc	r9,r6,r4	/* Compute end time */
 	addze	r8,r5
+#ifdef CONFIG_8xx
+2:	mftbu	r5
+#else
 2:	mfspr	r5, SPRN_TBRU
+#endif
 	cmpw	0,r5,r8
 	blt	2b
 	bgt	3f
+#ifdef CONFIG_8xx
+	mftb	r6
+#else
 	mfspr	r6, SPRN_TBRL
+#endif
 	cmpw	0,r6,r9
 	blt	2b
 3:	blr