Host/Linux: Implement GameMode

[kamfretoz]

Description of Changes

This PR implements support for Feral Interactive's GameMode. (Only for Linux)

GameMode is a daemon/lib combo for Linux that allows games to request a set of optimisations be temporarily applied to the host OS and/or a game process.

GameMode was designed primarily as a stop-gap solution to problems with the Intel and AMD CPU powersave or ondemand governors, but is now host to a range of optimisation features and configurations.

For more information, check out the Arch Linux Wiki.

You can find the settings on Settings -> Emulation -> Enable Feral GameMode

Note: You will need to have the actual gamemode's daemon itself installed on your system, otherwise PCSX2 will not do anything on its own.

PCSX2 will also detects if you have the daemon available and will automatically hide the setting if its not available on the running system.

NOTE 2: You have to enable advanced settings as well for the setting to show up. If this is too restrictive, further discussion are welcome.

2026-04-03.20-18-37.mp4

Rationale behind Changes

Hopefully better performance for those who needs it.

Closes #13237

Suggested Testing Steps

-1. Use Linux
0. Make sure GameMode is installed on your system

1. Open PCSX2 and open the log window, this is to check for gamemode related logs
2. Run any game (or the bios)
3. Check the logs and see if gamemode are properly kickstarted (search for "GameMode" string)

Also make sure nothing is broken on Windows and macOS side.

Did you use AI to help find, test, or implement this issue or feature?

Nop

[chaoticgd]

Found some problems, haven't benchmarked it.

[chaoticgd]

You should add the new game mode setting to the FSUI settings page too.

[kamfretoz]

You should add the new game mode setting to the FSUI settings page too.

Done.