md/md-bitmap: add 'sync_size' into struct md_bitmap_stats

md/md-bitmap: add 'sync_size' into struct md_bitmap_stats

[ Upstream commit ec6bb299c7c3dd4ca1724d13d5f5fae3ee54fc65 ]

To avoid dereferencing bitmap directly in md-cluster to prepare
inventing a new bitmap.

BTW, also fix following checkpatch warnings:

WARNING: Deprecated use of 'kmap_atomic', prefer 'kmap_local_page' instead
WARNING: Deprecated use of 'kunmap_atomic', prefer 'kunmap_local' instead

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240826074452.1490072-7-yukuai1@huaweicloud.com
Signed-off-by: Song Liu <song@kernel.org>
Stable-dep-of: 8d28d0ddb986 ("md/md-bitmap: Synchronize bitmap_get_stats() with bitmap lifetime")
Signed-off-by: Sasha Levin <sashal@kernel.org>