erofs: avoid pcpubuf.c inclusion if CONFIG_EROFS_FS_ZIP is off

The function of pcpubuf.c is just for low-latency decompression
algorithms (e.g. lz4).

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230515095758.10391-1-zbestahu@gmail.com


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