Savestates: Multi-threaded compression, use ZSTD

[elad335]

• Made saving extremely fast using multi-threaded compression, this was especially painful on AMD CPUs because their single thread performance vs multi thread performance difference is huge. But it also makes the life of Intel users much better too.
• Use ZSTD to compress savestates, a modern compression API with focus on performance with great compression ratios. So now RPCS3 supports both .SAVESTAT.gz and .SAVESTAT.zst inputs, but would create only .SAVESTAT.zst.
• Fix an SPU LLVM bug with savestates saving regarding access violations.
• Minor text fix in progress dialog. (showing "00s" for example instead of something clearer like "done", or "01s" instead of simply "1s")
• Fix sinking stores with GPR barriers in SPU LLVM, found when testing savestates with Demon's Souls with mr spaces.

Overall saving performance has been increased in more than 800%, reducing saving time from 30+ seconds to just 3 on Demon Souls gameplay which utilizes HDD1 cache so its savestates are heavy. And the savestate file size itself has been reduced in more than 100MB.