sh: pgtable: Fix missing prototypes

arch/sh/mm/pgtable.c:12:6: warning: no previous prototype for 'pgd_ctor' [-Wmissing-prototypes]
arch/sh/mm/pgtable.c:34:8: warning: no previous prototype for 'pgd_alloc' [-Wmissing-prototypes]
arch/sh/mm/pgtable.c:39:6: warning: no previous prototype for 'pgd_free' [-Wmissing-prototypes]
arch/sh/mm/pgtable.c:45:6: warning: no previous prototype for 'pud_populate' [-Wmissing-prototypes]
arch/sh/mm/pgtable.c:50:8: warning: no previous prototype for 'pmd_alloc_one' [-Wmissing-prototypes]
arch/sh/mm/pgtable.c:55:6: warning: no previous prototype for 'pmd_free' [-Wmissing-prototypes]

Make pgd_ctor() static, as it is only used in this file.
Include <asm/pgalloc.h> to fix the other warnings.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/aa1328ea3327d6685aab76d5787cb77c996052c0.1709326528.git.geert+renesas@glider.beSigned-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>

arch/sh/mm/pgtable.c

@@ -2,12 +2,14 @@
 #include <linux/mm.h>
 #include <linux/slab.h>
 
+#include <asm/pgalloc.h>
+
 static struct kmem_cache *pgd_cachep;
 #if PAGETABLE_LEVELS > 2
 static struct kmem_cache *pmd_cachep;
 #endif
 
-void pgd_ctor(void *x)
+static void pgd_ctor(void *x)
 {
 	pgd_t *pgd = x;