erofs: simplify compression configuration parser

erofs: simplify compression configuration parser

[ Upstream commit efb4fb02cef3ab410b603c8f0e1c67f61d55f542 ]

Move erofs_load_compr_cfgs() into decompressor.c as well as introduce
a callback instead of a hard-coded switch for each algorithm for
simplicity.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20231022130957.11398-1-xiang@kernel.org
Stable-dep-of: 118a8cf504d7 ("erofs: fix inconsistent per-file compression format")
Signed-off-by: Sasha Levin <sashal@kernel.org>