erofs-utils: prepare for per-(sub)file compress strategies

In order to adjust pclustersize on the per-(sub)file basis,
generating per-file map headers are needed instead.

In addition to that, we could use COMPACT_4B on the per-file
basis as well after this patch.

Link: https://lore.kernel.org/r/20210522043502.11975-2-xiang@kernel.org
Signed-off-by: Gao Xiang <xiang@kernel.org>
1 file changed