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/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 5c45787..fa8388e 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1174,12 +1174,19 @@
 
 #else /* __powerpc64__ */
 
+#if defined(CONFIG_8xx)
+#define mftbl()		({unsigned long rval;	\
+			asm volatile("mftbl %0" : "=r" (rval)); rval;})
+#define mftbu()		({unsigned long rval;	\
+			asm volatile("mftbu %0" : "=r" (rval)); rval;})
+#else
 #define mftbl()		({unsigned long rval;	\
 			asm volatile("mfspr %0, %1" : "=r" (rval) : \
 				"i" (SPRN_TBRL)); rval;})
 #define mftbu()		({unsigned long rval;	\
 			asm volatile("mfspr %0, %1" : "=r" (rval) : \
 				"i" (SPRN_TBRU)); rval;})
+#endif
 #endif /* !__powerpc64__ */
 
 #define mttbl(v)	asm volatile("mttbl %0":: "r"(v))