fs: ext4: do not write on filesystem with metadata_csum feature

U-Boot doesn't support metadata_csum feature. Writing to filesystem with
metadata_csum feature makes the filesystem corrupted and unbootable by
Linux:

[    2.527495] EXT4-fs (mmcblk0p2): ext4_check_descriptors: Checksum for group 0 failed (52188!=0)
[    2.537421] EXT4-fs (mmcblk0p2): ext4_check_descriptors: Checksum for group 1 failed (5262!=0)
...
[    2.653308] EXT4-fs (mmcblk0p2): ext4_check_descriptors: Checksum for group 14 failed (42611!=0)
[    2.662179] EXT4-fs (mmcblk0p2): ext4_check_descriptors: Checksum for group 15 failed (21527!=0)
[    2.687920] JBD2: journal checksum error
[    2.691982] EXT4-fs (mmcblk0p2): error loading journal
[    2.698292] VFS: Cannot open root device "mmcblk0p2" or unknown-block(179,2): error -74

Don't write to filesystem with meatadata_csum feature to not corrupt the
filesystem.

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
diff --git a/include/ext4fs.h b/include/ext4fs.h
index bb55639..2421011 100644
--- a/include/ext4fs.h
+++ b/include/ext4fs.h
@@ -32,6 +32,7 @@
 #define EXT4_EXTENTS_FL		0x00080000 /* Inode uses extents */
 #define EXT4_EXT_MAGIC			0xf30a
 #define EXT4_FEATURE_RO_COMPAT_GDT_CSUM	0x0010
+#define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM 0x0400
 #define EXT4_FEATURE_INCOMPAT_EXTENTS	0x0040
 #define EXT4_FEATURE_INCOMPAT_64BIT	0x0080
 #define EXT4_INDIRECT_BLOCKS		12