dosfstools: add backported patch for honouring SOURCE_DATE_EPOCH

dosfstools: add backported patch for honouring SOURCE_DATE_EPOCH

Currently, file system images created with mkfs.vfat are not
reproducible, because both the file system creation time and the
volume id are derived from the current time.

Upstream has added a patch for deriving those from SOURCE_DATE_EPOCH,
when defined, many years ago, but unfortunately there is no official
release containing that patch.

The issue [1] is 2.5 years old, so there's no reason to believe such a
release would be just around the corner.

The patch applies cleanly, and e.g. Arch Linux already uses this exact
combination of source tarball and this single patch [2], so I think
this should be ok. It certainly works for the images I've tested on.

[1] https://github.com/dosfstools/dosfstools/issues/179
[2] https://gitlab.archlinux.org/archlinux/packaging/packages/dosfstools/-/blob/main/PKGBUILD?ref_type=heads

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>