powerpc: Use feature bit for RTC presence rather than timebase presence

All PowerPC CPUs other than the original PPC601 have a timebase
register rather than the "real-time clock" (RTC) register that the
PPC601 (and the original POWER and POWER2 CPUs) had.  Currently
we have a CPU feature bit to indicate the presence of the timebase,
but it makes more sense to use a bit to indicate the unusual
situation rather than the common situation.  This therefore defines
a CPU_FTR_USE_RTC bit in place of the CPU_FTR_USE_TB bit, and
arranges for it to be set on PPC601 systems.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/time.h

@@ -46,7 +46,7 @@ struct div_result {
 /* Accessor functions for the timebase (RTC on 601) registers. */
 /* If one day CONFIG_POWER is added just define __USE_RTC as 1 */
 #ifdef CONFIG_6xx
-#define __USE_RTC()	(!cpu_has_feature(CPU_FTR_USE_TB))
+#define __USE_RTC()	(cpu_has_feature(CPU_FTR_USE_RTC))
 #else
 #define __USE_RTC()	0
 #endif

arch/powerpc/kernel/dt_cpu_ftrs.c

@@ -54,8 +54,7 @@ struct dt_cpu_feature {
 };
 
 #define CPU_FTRS_BASE \
-	   (CPU_FTR_USE_TB | \
-	    CPU_FTR_LWSYNC | \
+	   (CPU_FTR_LWSYNC | \
 	    CPU_FTR_FPU_UNAVAILABLE |\
 	    CPU_FTR_NODSISRALIGN |\
 	    CPU_FTR_NOEXECUTE |\

arch/powerpc/kernel/vdso.c

@@ -99,26 +99,28 @@ static struct vdso_patch_def vdso_patches[] = {
 		CPU_FTR_COHERENT_ICACHE, CPU_FTR_COHERENT_ICACHE,
 		"__kernel_sync_dicache", "__kernel_sync_dicache_p5"
 	},
+#ifdef CONFIG_PPC32
 	{
-		CPU_FTR_USE_TB, 0,
+		CPU_FTR_USE_RTC, CPU_FTR_USE_RTC,
 		"__kernel_gettimeofday", NULL
 	},
 	{
-		CPU_FTR_USE_TB, 0,
+		CPU_FTR_USE_RTC, CPU_FTR_USE_RTC,
 		"__kernel_clock_gettime", NULL
 	},
 	{
-		CPU_FTR_USE_TB, 0,
+		CPU_FTR_USE_RTC, CPU_FTR_USE_RTC,
 		"__kernel_clock_getres", NULL
 	},
 	{
-		CPU_FTR_USE_TB, 0,
+		CPU_FTR_USE_RTC, CPU_FTR_USE_RTC,
 		"__kernel_get_tbfreq", NULL
 	},
 	{
-		CPU_FTR_USE_TB, 0,
+		CPU_FTR_USE_RTC, CPU_FTR_USE_RTC,
 		"__kernel_time", NULL
 	},
+#endif
 };
 
 /*