nds32: Fix xfs_buf built failed by export invalidate_kernel_vmap_range and flush_kernel_vmap_range

It broke the 'allmodconfig' build.
fs/xfs/xfs_buf.c: In function 'xfs_buf_bio_end_io':
fs/xfs/xfs_buf.c:1242:3: error: implicit declaration of function 'invalidate_kernel_vmap_range' [-Werror=implicit-function-declaration]
   invalidate_kernel_vmap_range(bp->b_addr, xfs_buf_vmap_len(bp));
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
fs/xfs/xfs_buf.c: In function 'xfs_buf_ioapply_map':
fs/xfs/xfs_buf.c:1312:4: error: implicit declaration of function 'flush_kernel_vmap_range' [-Werror=implicit-function-declaration]
    flush_kernel_vmap_range(bp->b_addr,
    ^~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Greentime Hu <greentime@andestech.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/nds32/include/asm/cacheflush.h

@@ -32,6 +32,8 @@ void flush_anon_page(struct vm_area_struct *vma,
 
 #define ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE
 void flush_kernel_dcache_page(struct page *page);
+void flush_kernel_vmap_range(void *addr, int size);
+void invalidate_kernel_vmap_range(void *addr, int size);
 void flush_icache_range(unsigned long start, unsigned long end);
 void flush_icache_page(struct vm_area_struct *vma, struct page *page);
 #define flush_dcache_mmap_lock(mapping)   xa_lock_irq(&(mapping)->i_pages)

arch/nds32/mm/cacheflush.c

@@ -273,6 +273,24 @@ void flush_kernel_dcache_page(struct page *page)
 	local_irq_restore(flags);
 }
 
+void flush_kernel_vmap_range(void *addr, int size)
+{
+	unsigned long flags;
+	local_irq_save(flags);
+	cpu_dcache_wb_range((unsigned long)addr, (unsigned long)addr +  size);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL(flush_kernel_vmap_range);
+
+void invalidate_kernel_vmap_range(void *addr, int size)
+{
+	unsigned long flags;
+	local_irq_save(flags);
+	cpu_dcache_inval_range((unsigned long)addr, (unsigned long)addr + size);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL(invalidate_kernel_vmap_range);
+
 void flush_icache_range(unsigned long start, unsigned long end)
 {
 	unsigned long line_size, flags;