arm64: mm: Add pgd_page to support RCU fast_gup
arm64: mm: Add pgd_page to support RCU fast_gup

This patch adds pgd_page definition in order to keep supporting
HAVE_GENERIC_RCU_GUP configuration. In addition, it changes pud_page
expression to align with pmd_page for readability.

An introduction of pgd_page resolves the following build breakage
under 4KB + 4Level memory management combo.

mm/gup.c: In function 'gup_huge_pgd':
mm/gup.c:889:2: error: implicit declaration of function 'pgd_page' [-Werror=implicit-function-declaration]
  head = pgd_page(orig);
  ^
mm/gup.c:889:7: warning: assignment makes pointer from integer without a cast
  head = pgd_page(orig);

Cc: Will Deacon <b913f13ef92ac157955c954ccaaff7be065faba4@arm.com>
Cc: Steve Capper <20bdc7169d3cb6e97bf912a5efd111f83cbbb42b@linaro.org>
Signed-off-by: Jungseok Lee <4e51fafd9bd9d4bbb75574120b58713dc271cae0@gmail.com>
[15ce75b290ebaf27c3f9fd73ab848685ed3d8261@arm.com: remove duplicate pmd_page definition]
Signed-off-by: Catalin Marinas <15ce75b290ebaf27c3f9fd73ab848685ed3d8261@arm.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs