erofs: add SEEK_{DATA,HOLE} support

Many userspace programs (including erofs-utils itself) use SEEK_DATA /
SEEK_HOLE to parse hole extents in addition to FIEMAP.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241011065128.2097377-1-hsiangkao@linux.alibaba.com