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

Commit beb2dc0a7a 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>

arch/powerpc/include/asm/timex.h

@@ -29,7 +29,11 @@ static inline cycles_t get_cycles(void)
 	ret = 0;
 
 	__asm__ __volatile__(
+#ifdef CONFIG_8xx
+		"97:	mftb %0\n"
+#else
 		"97:	mfspr %0, %2\n"
+#endif
 		"99:\n"
 		".section __ftr_fixup,\"a\"\n"
 		".align 2\n"
@@ -41,7 +45,11 @@ static inline cycles_t get_cycles(void)
 		"	.long 0\n"
 		"	.long 0\n"
 		".previous"
+#ifdef CONFIG_8xx
+		: "=r" (ret) : "i" (CPU_FTR_601));
+#else
 		: "=r" (ret) : "i" (CPU_FTR_601), "i" (SPRN_TBRL));
+#endif
 	return ret;
 #endif
 }