ext2: Deprecate DAX

Since PMEM didn't quite lift off, DAX isn't as widely used as we
originally hoped. Thus it doesn't seem warranted to support
implementation of DAX in ext2 driver when the same filesystem can be
accessed through ext4 driver as a "simple implementation". Just
deprecate DAX support in ext2 targetting completely dropping the code at
the end of 2025.

Link: https://lore.kernel.org/all/uiu7rcmtooxgbscaiiim7czqsca52bgrt6aiszsafq7jj4n3e7@ge6mfzcmnorl


Signed-off-by: Jan Kara <jack@suse.cz>