fs: fat: support mkdir

In this patch, mkdir support is added to FAT file system.
A newly created directory contains only "." and ".." entries.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

fs/fs.c

@@ -164,14 +164,15 @@ static struct fstype_info fstypes[] = {
 		.read = fat_read_file,
 #ifdef CONFIG_FAT_WRITE
 		.write = file_fat_write,
+		.mkdir = fat_mkdir,
 #else
 		.write = fs_write_unsupported,
+		.mkdir = fs_mkdir_unsupported,
 #endif
 		.uuid = fs_uuid_unsupported,
 		.opendir = fat_opendir,
 		.readdir = fat_readdir,
 		.closedir = fat_closedir,
-		.mkdir = fs_mkdir_unsupported,
 	},
 #endif
 #ifdef CONFIG_FS_EXT4