macOS: IOKit not linked when Cocoa Video backend is used

[Jan200101]

the cocoa video backend makes use of functions like IOPMAssertionRelease which, according to apples documentation, is provided by IOKit

If SDL_FRAMEWORK_IOKIT is never set (by disabling SDL_JOYSTICK, SDL_HAPIC and SDL_POWER) it will never be used during linking and the cocoa backend fails to link.

I'm not 100% sure if this is correct and only deducted this from CI output, I believe the right fix would be simple to set SDL_FRAMEWORK_IOKIT to 1 in the CheckCOCOA macro

[icculus]

(There's never a reason to not link to IOKit on macOS, so maybe it's safer to just always link to it regardless of backends enabled...?)