fs/ext2: fixes for ext2r0 with host-e2fsprogs >= 1.47.2

Since Buildroot commit [1] "package/e2fsprogs: bump version to
1.47.2", running the runtime test tests.fs.test_ext.TestExt2 with the
command:

    utils/docker-run support/testing/run-tests \
        -d dl -o output_folder \
        tests.fs.test_ext.TestExt2
    tail output_folder/TestExt2-build.log

Fails with error in the log:

    mkfs.ext2: the -r option has been removed.

    If you really need compatibility with pre-1995 Linux systems, use the
    command-line option "-E revision=0".

Upstream commit [2] "tune2fs: replace the -r option with -E
revision=<fs-rev>" removed this option.

This commit fixes the issue by using the new form with -E. Also,
BR2_TARGET_ROOTFS_EXT2_MKFS_OPTIONS has a default value to "-O
^64bit". Passing a "-O ..." option now generates an error when a
ext2r0 filesystem is created (because this revision does not support
ext2 filesystem feature options). This commit sets this default value
only if BR2_TARGET_ROOTFS_EXT2_2r0 is not set.

Fixes: [3]

[1] https://gitlab.com/buildroot.org/buildroot/-/commit/db459859fa3c8fb7a2c0c8b8616637644d9c12bf
[2] https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/commit/?id=3fffe9dd6be5a5ed77755cf23c267b4afd1e7651
[3] https://gitlab.com/buildroot.org/buildroot/-/jobs/8830670170

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

fs/ext2/Config.in

@@ -85,7 +85,8 @@ config BR2_TARGET_ROOTFS_EXT2_RESBLKS
 
 config BR2_TARGET_ROOTFS_EXT2_MKFS_OPTIONS
 	string "additional mke2fs options"
-	default "-O ^64bit"
+	# Note: ext2 rev0 does not support filesystem options.
+	default "-O ^64bit" if !BR2_TARGET_ROOTFS_EXT2_2r0
 	help
 	  Specify a space-separated list of mke2fs options, including
 	  any ext2/3/4 filesystem features.
@@ -100,7 +101,8 @@ config BR2_TARGET_ROOTFS_EXT2_MKFS_OPTIONS
 	  support. This default value has been chosen because U-Boot
 	  versions before 2017.02 don't support this filesystem
 	  option: using it may make the filesystem unreadable by
-	  U-Boot.
+	  U-Boot. Note: this default does not apply to the old ext2
+	  (rev0) which does not support filesystem options.
 
 choice
 	prompt "Compression method"

fs/ext2/ext2.mk

@@ -18,7 +18,7 @@ ROOTFS_EXT2_LABEL = $(subst ",,$(BR2_TARGET_ROOTFS_EXT2_LABEL))
 
 ROOTFS_EXT2_OPTS = \
 	-d $(TARGET_DIR) \
-	-r $(BR2_TARGET_ROOTFS_EXT2_REV) \
+	-E revision=$(BR2_TARGET_ROOTFS_EXT2_REV) \
 	-N $(BR2_TARGET_ROOTFS_EXT2_INODES) \
 	-m $(BR2_TARGET_ROOTFS_EXT2_RESBLKS) \
 	-L "$(ROOTFS_EXT2_LABEL)" \