mm: add p{g/4}d_leaf() in asm-generic/pgtable-nop{4/u}d.h

Commit 2c8a81dc ("riscv/mm: fix two page table check related issues")
added pud_leaf() in include/asm-generic/pgtable-nopmd.h

Do the same for p4d_leaf() and pgd_leaf() to avoid getting them
erroneously defined by architectures that do not implement the related
page level.

Link: https://lkml.kernel.org/r/f69941b076bf8fec89b6bec5573fdb79483c2a75.1720597744.git.christophe.leroy@csgroup.eu


Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>