GS: Further state cleanup + fixes for older dump compatibility

[refractionpcsx2]

Description of Changes

Fixes compatibility with old savestates + remove PRMODE which is no longer used. Also bumps savestate version.

Rationale behind Changes

Recent changes temporarily broke compat with older states since it was merged before the PR was completely ready.

Suggested Testing Steps

Test GS Dumps and savestates from PCSX2 to make sure they all work ok.

[prafullpcsx2]

Still getting this message with old gsdumpgui while trying to run freshly made gsdump:-

And still getting black screen with pcsx2 integrated gs debugger ( dev 1961 and older).

[refractionpcsx2]

Of course, you can't go backwards.. You get backwards compat from old versions with the new version, but you will never be able to make a new gs dump and run it on the old gsdumpgui. I'm afraid that's dead unless people use an old version of pcsx2

[prafullpcsx2]

Thanks for explanation. That means we lose ability to check for regressions unless we are going to ask users to make gs dumps using old pcsx2 versions. I hope the gains are far more than this loss.

[refractionpcsx2]

Why can't you use the gsdump too in the new version?

Edit: nevermind, I know why, because of testing old GSDX versions. I think we're just gonna have to lump it so we can move forward, 1.6 will just need to be used if you need to regression test.