powerpc/64e: Rewrite p4d_populate() as a static inline function

Rewrite p4d_populate() as a static inline function instead of
a macro.

This change allows typechecking and would have helped detecting
a recently found bug in map_kernel_page().

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1b416f8a8fe1bc3f4e01175680ce310b7eb3a1e4.1655974565.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/64/pgalloc.h

@@ -15,7 +15,10 @@ struct vmemmap_backing {
 };
 extern struct vmemmap_backing *vmemmap_list;
 
-#define p4d_populate(MM, P4D, PUD)	p4d_set(P4D, (unsigned long)PUD)
+static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4d, pud_t *pud)
+{
+	p4d_set(p4d, (unsigned long)pud);
+}
 
 static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
 {