Add the mount parameter 'threads=' for squashfs

configname: CONFIG_SQUASHFS_MOUNT_DECOMP_THREADS

Linux Kernel Configuration
└─>File systems
└─>Miscellaneous filesystems
└─>Add the mount parameter 'threads=' for squashfs
In linux kernel since version 6.2 (release Date: 2023-02-19)  
Use threads= to set the decompression parallel mode and the number of threads.
If SQUASHFS_CHOICE_DECOMP_BY_MOUNT=y
threads=<single|multi|percpu|1|2|3|...>
else
threads=<2|3|...>
The upper limit is num_online_cpus() * 2.