Create default mapping for unknown control pads in SDL's controller database

[neilmunday]

Updated SDL/SDLJoystick.cpp in response to #9987

Summary:

If a control pad is not found in SDL's game controller database then a default mapping (based on the Sony PlayStation 3 Dual Shock controller) will be created and added to the in-memory database. Note: this new mapping is temporary and is not written to the control pad database.

[hrydgard]

Nice. The occasional wrong button mapping is better than it working at all for unknown joysticks. Only drawback I can see is that motivation for adding new known-good mappings might be smaller.. oh well.

[carlsmith]

Button mappings are easy to fix. The analogue sticks are the problem. There are third party apps that will map control pad inputs to keyboard keys reliably, and that works perfectly with PPSSPP, but they can only map the analogue sticks to binary keys or buttons, like D-pads.

At the moment, I can only use PPSSPP with games that work with a D-pad, like Wipeout, even though I'm using a pad with analogue sticks.