selftests/powerpc: Move pick_online_cpu() up into utils.c

We want to use this in another test, so make it available at the top of
the powerpc selftests tree.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/utils.h

@@ -22,6 +22,7 @@ typedef uint8_t u8;
 
 int test_harness(int (test_function)(void), char *name);
 extern void *get_auxv_entry(int type);
+int pick_online_cpu(void);
 
 static inline bool have_hwcap2(unsigned long ftr2)
 {