x86: update populate_extra_pte() and add populate_extra_pmd()

Impact: minor change to populate_extra_pte() and addition of pmd flavor

Update populate_extra_pte() to return pointer to the pte_t for the
specified address and add populate_extra_pmd() which only populates
till the pmd and returns pointer to the pmd entry for the address.

For 64bit, pud/pmd/pte fill functions are separated out from
set_pte_vaddr[_pud]() and used for set_pte_vaddr[_pud]() and
populate_extra_{pte|pmd}().

Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index dd91c25..46312eb 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -402,7 +402,8 @@
 
 /* Install a pte for a particular vaddr in kernel space. */
 void set_pte_vaddr(unsigned long vaddr, pte_t pte);
-void populate_extra_pte(unsigned long vaddr);
+pmd_t *populate_extra_pmd(unsigned long vaddr);
+pte_t *populate_extra_pte(unsigned long vaddr);
 
 #ifdef CONFIG_X86_32
 extern void native_pagetable_setup_start(pgd_t *base);