f2fs: add MODULE_SOFTDEP to ensure crc32 is included in the initramfs

As marcosfrm reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=213089



Initramfs generators rely on "pre" softdeps (and "depends") to include
additional required modules.

F2FS does not declare "pre: crc32" softdep. Then every generator (dracut,
mkinitcpio...) has to maintain a hardcoded list for this purpose.

Hence let's use MODULE_SOFTDEP("pre: crc32") in f2fs code.

Fixes: 43b6573b ("f2fs: use cryptoapi crc32 functions")
Reported-by: marcosfrm <marcosfrm@gmail.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>