The information whether a specific joystick can be used as a gamepad is
not going to change every frame, so we can cache the result into a
variable.
This dramatically reduces the performance impact of SDL2 on small
embedded devices, since the code path that is now avoided was quite
heavy.
Fixes#4229.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
1542300a89