[POWERPC] Don't expose clock vDSO functions when CPU has no timebase

We forgot to remove the clock_gettime, clock_getres and get_tbfreq vDSO
calls on CPUs that have no timebase such as 601 or 403 (old CPUs that have
different mechanisms and for which the vDSO code will not work properly).
This fixes it.

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Paul Mackerras <[e-mail]>

arch/powerpc/kernel/vdso.c

···
 		CPU_FTR_USE_TB, 0,
 		"__kernel_gettimeofday", NULL
 	},
+	{
+		CPU_FTR_USE_TB, 0,
+		"__kernel_clock_gettime", NULL
+	},
+	{
+		CPU_FTR_USE_TB, 0,
+		"__kernel_clock_getres", NULL
+	},
+	{
+		CPU_FTR_USE_TB, 0,
+		"__kernel_get_tbfreq", NULL
+	},
 };
 
 /*