riscv: mm: fix build errors caused by mk_pmd()

With "riscv: mm: add THP support on 64-bit", mk_pmd() function
introduce build errors,
1.build with CONFIG_ARCH_RV32I=y:
arch/riscv/include/asm/pgtable.h: In function 'mk_pmd':
arch/riscv/include/asm/pgtable.h:513:9: error: implicit declaration of function 'pfn_pmd';
 did you mean 'pfn_pgd'? [-Werror=implicit-function-declaration]

2.build with CONFIG_SPARSEMEM=y && CONFIG_SPARSEMEM_VMEMMAP=n
arch/riscv/include/asm/pgtable.h: In function 'mk_pmd':
include/asm-generic/memory_model.h:64:14: error: implicit declaration of function 'page_to_section';
 did you mean 'present_section'? [-Werror=implicit-function-declaration]

Move the definition of mk_pmd to pgtable-64.h to fix the first error.
Use macro definition instead of inline function for mk_pmd
to fix the second problem. It is similar to the mk_pte macro.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Nanyong Sun <sunnanyong@huawei.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/pgtable-64.h

@@ -79,6 +79,8 @@ static inline unsigned long _pmd_pfn(pmd_t pmd)
 	return pmd_val(pmd) >> _PAGE_PFN_SHIFT;
 }
 
+#define mk_pmd(page, prot)    pfn_pmd(page_to_pfn(page), prot)
+
 #define pmd_ERROR(e) \
 	pr_err("%s:%d: bad pmd %016lx.\n", __FILE__, __LINE__, pmd_val(e))
 

arch/riscv/include/asm/pgtable.h

@@ -516,11 +516,6 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
 	return ((__pmd_to_phys(pmd) & PMD_MASK) >> PAGE_SHIFT);
 }
 
-static inline pmd_t mk_pmd(struct page *page, pgprot_t prot)
-{
-	return pfn_pmd(page_to_pfn(page), prot);
-}
-
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 {
 	return pte_pmd(pte_modify(pmd_pte(pmd), newprot));