powerpc/mm/64s: Fix no previous prototype warning

As reported by lkp:

  arch/powerpc/mm/book3s64/radix_tlb.c:646:6: warning: no previous
  prototype for function 'exit_lazy_flush_tlb'

Fix it by moving the prototype into the existing header.

Fixes: 032b7f0893 ("powerpc/64s/radix: serialize_against_pte_lookup IPIs trim mm_cpumask")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210210130804.3190952-2-mpe@ellerman.id.au

arch/powerpc/mm/book3s64/internal.h

@@ -15,4 +15,6 @@ static inline bool stress_slb(void)
 
 void slb_setup_new_exec(void);
 
+void exit_lazy_flush_tlb(struct mm_struct *mm, bool always_flush);
+
 #endif /* ARCH_POWERPC_MM_BOOK3S64_INTERNAL_H */

arch/powerpc/mm/book3s64/pgtable.c

@@ -20,6 +20,8 @@
 #include <mm/mmu_decl.h>
 #include <trace/events/thp.h>
 
+#include "internal.h"
+
 unsigned long __pmd_frag_nr;
 EXPORT_SYMBOL(__pmd_frag_nr);
 unsigned long __pmd_frag_size_shift;
@@ -79,8 +81,6 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 	return set_pte_at(mm, addr, pmdp_ptep(pmdp), pmd_pte(pmd));
 }
 
-void exit_lazy_flush_tlb(struct mm_struct *mm, bool always_flush);
-
 static void do_serialize(void *arg)
 {
 	/* We've taken the IPI, so try to trim the mask while here */

arch/powerpc/mm/book3s64/radix_tlb.c

@@ -18,6 +18,8 @@
 #include <asm/cputhreads.h>
 #include <asm/plpar_wrappers.h>
 
+#include "internal.h"
+
 #define RIC_FLUSH_TLB 0
 #define RIC_FLUSH_PWC 1
 #define RIC_FLUSH_ALL 2