riscv: fix build error when CONFIG_SMP is disabled

Fix build error when disable CONFIG_SMP:
mm/pgtable-generic.o: In function `.L19':
pgtable-generic.c:(.text+0x42): undefined reference to `flush_pmd_tlb_range'
mm/pgtable-generic.o: In function `pmdp_huge_clear_flush':
pgtable-generic.c:(.text+0x6c): undefined reference to `flush_pmd_tlb_range'
mm/pgtable-generic.o: In function `pmdp_invalidate':
pgtable-generic.c:(.text+0x162): undefined reference to `flush_pmd_tlb_range'

Fixes: e88b3331 ("riscv: mm: add THP support on 64-bit")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Bixuan Cui <cuibixuan@huawei.com>
Acked-by: Nanyong Sun <sunnanyong@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/pgtable.h

@@ -623,11 +623,6 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
 {
 	return __pmd(atomic_long_xchg((atomic_long_t *)pmdp, pmd_val(pmd)));
 }
-
-#define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
-void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
-			unsigned long end);
-
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 /*

arch/riscv/include/asm/tlbflush.h

@@ -33,6 +33,11 @@ void flush_tlb_mm(struct mm_struct *mm);
 void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr);
 void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 		     unsigned long end);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
+void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
+			unsigned long end);
+#endif
 #else /* CONFIG_SMP && CONFIG_MMU */
 
 #define flush_tlb_all() local_flush_tlb_all()