powerpc/vdso: Cleanup vdso.h

Rename the guard define to _ASM_POWERPC_VDSO_H

And remove useless #ifdef __KERNEL__
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9902590d410cd1c2afa48b83b277faf0711f07b2.1601197618.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/vdso.h

 /* SPDX-License-Identifier: GPL-2.0 */
-#ifndef __PPC64_VDSO_H__
-#define __PPC64_VDSO_H__
-
-#ifdef __KERNEL__
+#ifndef _ASM_POWERPC_VDSO_H
+#define _ASM_POWERPC_VDSO_H
 
 /* Default map addresses for 32bit vDSO */
 #define VDSO32_MBASE	0x100000
@@ -54,6 +52,4 @@ int vdso_getcpu_init(void);
 
 #endif /* __ASSEMBLY__ */
 
-#endif /* __KERNEL__ */
-
-#endif /* __PPC64_VDSO_H__ */
+#endif /* _ASM_POWERPC_VDSO_H */