Implemented SDATA unpacking

I have placed the sdata_unpack and sdata_check functions in
/rpcs3/Emu/SysCalls/Modules/sys_fs.cpp. The a temporary unpacked file is
generated in /dev_hdd1/ which according to the information I found on
the Internet, it's the system cache, so I guess it's not a bad place at
all for putting this. I hope this is ok.