erofs: add sysfs node to drop internal caches

Add a sysfs node to drop compression-related caches, currently used to
drop in-memory pclusters and cached compressed folios.

Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241113041148.749129-1-guochunhai@vivo.com


Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>