erofs: apply proper VMA alignment for memory mapped files on THP

[ Upstream commit 4127caee89612a84adedd78c9453089138cd5afe ]

There are mainly two reasons that thp_get_unmapped_area() should be
used for EROFS as other filesystems:

 - It's needed to enable PMD mappings as a FSDAX filesystem, see
   commit 74d2fad133 ("thp, dax: add thp_get_unmapped_area for pmd
   mappings");

 - It's useful together with large folios and
   CONFIG_READ_ONLY_THP_FOR_FS which enable THPs for mmapped files
   (e.g. shared libraries) even without FSDAX.  See commit 1854bc6e24
   ("mm/readahead: Align file mappings for non-DAX").

Fixes: 06252e9ce0 ("erofs: dax support for non-tailpacking regular file")
Fixes: ce529cc25b ("erofs: enable large folios for iomap mode")
Fixes: e6687b8922 ("erofs: enable large folios for fscache mode")
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240306053138.2240206-1-hsiangkao@linux.alibaba.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/erofs/data.c

@@ -340,4 +340,5 @@ const struct file_operations erofs_file_fops = {
 	.read_iter	= erofs_file_read_iter,
 	.mmap		= erofs_file_mmap,
 	.splice_read	= generic_file_splice_read,
+	.get_unmapped_area = thp_get_unmapped_area,
 };