erofs: support I/O submission for sub-page compressed blocks

Add a basic I/O submission path first to support sub-page blocks:

 - Temporary short-lived pages will be used entirely;

 - In-place I/O pages can be used partially, but compressed pages need
   to be able to be mapped in contiguous virtual memory.

As a start, currently cache decompression is explicitly disabled for
sub-page blocks, which will be supported in the future.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20231206091057.87027-2-hsiangkao@linux.alibaba.com