Use percpu multiple decompressors for parallel I/O

configname: CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU

Decompressor parallelisation options
└─>Use percpu multiple decompressors for parallel I/O
In linux kernel since version 3.10 (release Date: 2013-06-30)  
By default Squashfs uses a single decompressor but it gives
poor performance on parallel I/O workloads when using multiple CPU
machines due to waiting on decompressor availability.

This decompressor implementation uses a maximum of one
decompressor per core. It uses percpu variables to ensure
decompression is load-balanced across the cores.