sparc64: add the missing pgd_page definition

sparc64 only had pgd_page_vaddr, but not pgd_page.

[hch@lst.de: fix sparc64 build]
  Link: http://lkml.kernel.org/r/20190626131318.GA5101@lst.de
Link: http://lkml.kernel.org/r/20190625143715.1689-8-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: David Miller <davem@davemloft.net>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Rich Felker <dalias@libc.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/sparc/include/asm/pgtable_64.h

@@ -864,6 +864,9 @@ static inline unsigned long pud_page_vaddr(pud_t pud)
 #define pgd_present(pgd)		(pgd_val(pgd) != 0U)
 #define pgd_clear(pgdp)			(pgd_val(*(pgdp)) = 0UL)
 
+/* only used by the stubbed out hugetlb gup code, should never be called */
+#define pgd_page(pgd)			NULL
+
 static inline unsigned long pud_large(pud_t pud)
 {
 	pte_t pte = __pte(pud_val(pud));