x86/vdso: Fix -Wmissing-prototypes warnings

Fix those:

  In file included from arch/x86/entry/vdso/vdso32/vclock_gettime.c:4:
arch/x86/entry/vdso/vdso32/../vclock_gettime.c:70:5: warning: no previous prototype for ‘__vdso_clock_gettime64’ [-Wmissing-prototypes]
   70 | int __vdso_clock_gettime64(clockid_t clock, struct __kernel_timespec *ts)
      |

In file included from arch/x86/entry/vdso/vdso32/vgetcpu.c:3:
arch/x86/entry/vdso/vdso32/../vgetcpu.c:13:1: warning: no previous prototype for ‘__vdso_getcpu’ [-Wmissing-prototypes]
   13 | __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
      | ^~~~~~~~~~~~~
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/202302070742.iYcnoJwk-lkp@intel.com

arch/x86/include/asm/vdso/gettimeofday.h

@@ -318,6 +318,8 @@ u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult)
 }
 #define vdso_calc_delta vdso_calc_delta
 
+int __vdso_clock_gettime64(clockid_t clock, struct __kernel_timespec *ts);
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ASM_VDSO_GETTIMEOFDAY_H */

arch/x86/include/asm/vdso/processor.h

@@ -18,6 +18,10 @@ static __always_inline void cpu_relax(void)
 	rep_nop();
 }
 
+struct getcpu_cache;
+
+notrace long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused);
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __ASM_VDSO_PROCESSOR_H */