Support input from all controller channels.

[yo1dog]

Adds listening to input from all controller channels instead of just 0. This restores functionality for those w/o a functioning P1 controller port.

Many lines touched but functionally a small change. The meat is in input.c. The rest is simply replacing PAD_ButtonsHeld(0) and PAD_ButtonsDown(0) with padsButtonsHeld() and padsButtonsDown().

Implementation is straightforward for buttons: bitwise-or the button states of all controllers.

Tested on my personal DOL-101. Works great.