Savedata: Respect IO timing method setting

[unknownbrackets]

With this, configuring IO timing method = Host will probably dodge any stutters on scoped storage save/load, but may be more hazardous if there's some game that expects specific timing. See #13847.

The current timing (always completes in one frame) is definitely wrong, but this is a quick change to validate my assumption that changes here could be an improvement. We should improve it, but that seems a bit more dangerous right now than extending this setting (which already has possible instability) to savedata, which it really should've always included.

-[Unknown]

[hrydgard]

Let's just get this in, since (for now) it's host timing mode only.

I guess for fixed timing modes, we should later have a fixed delay of a couple more frames maybe, to get a better chance of covering I/O spikes.