selftests: vDSO: use parse_vdso.h in vdso_test_abi

Don't duplicate parse_vdso function prototypes, include
the header instead.

Fixes: 693f5ca08c ("kselftest: Extend vDSO selftest")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tools/testing/selftests/vDSO/vdso_test_abi.c

@@ -21,10 +21,7 @@
 #include "../kselftest.h"
 #include "vdso_config.h"
 #include "vdso_call.h"
-
-extern void *vdso_sym(const char *version, const char *name);
-extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
-extern void vdso_init_from_auxv(void *auxv);
+#include "parse_vdso.h"
 
 static const char *version;
 static const char **name;