wire up vdso clock_gettime for powerpc, powerpc64, and s390x

symbol names and versions obtained from vdso(7) man page.

arch/powerpc/syscall_arch.h

@@ -92,3 +92,9 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 
 #define SO_RCVTIMEO_OLD  18
 #define SO_SNDTIMEO_OLD  19
+
+#define VDSO_USEFUL
+#define VDSO_CGT32_SYM "__kernel_clock_gettime"
+#define VDSO_CGT32_VER "LINUX_2.6.15"
+#define VDSO_CGT_SYM "__kernel_clock_gettime64"
+#define VDSO_CGT_VER "LINUX_5.11"

arch/powerpc64/syscall_arch.h

@@ -88,3 +88,7 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 
 #define SO_RCVTIMEO_OLD  18
 #define SO_SNDTIMEO_OLD  19
+
+#define VDSO_USEFUL
+#define VDSO_CGT_SYM "__kernel_clock_gettime"
+#define VDSO_CGT_VER "LINUX_2.6.15"

arch/s390x/syscall_arch.h

@@ -72,3 +72,7 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 	register long r7 __asm__("r7") = f;
 	__asm_syscall("+r"(r2), "r"(r1), "r"(r3), "r"(r4), "r"(r5), "r"(r6), "r"(r7));
 }
+
+#define VDSO_USEFUL
+#define VDSO_CGT_SYM "__kernel_clock_gettime"
+#define VDSO_CGT_VER "LINUX_2.6.29"