erofs: use `struct erofs_device_info` for the primary device

erofs: use `struct erofs_device_info` for the primary device

[ Upstream commit 7b00af2c5414dc01e0718deef7ead81102867636 ]

Instead of just listing each one directly in `struct erofs_sb_info`
except that we still use `sb->s_bdev` for the primary block device.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241216125310.930933-2-hsiangkao@linux.alibaba.com
Stable-dep-of: 6422cde1b0d5 ("erofs: use buffered I/O for file-backed mounts by default")
Signed-off-by: Sasha Levin <sashal@kernel.org>