We would need a generic "Keyboards" credit (which includes various keyboard (1) instruments). The term often used in liners in german is "Tasteninstrumente" (2). Also to be found: "claviers" in french, "tastiere" in italian credits. Translating all these with just a singular "keyboard" is most unsatisfactory when it obviously can include everything from grand piano or organ to sythesizers...

We already have a similar generic/plural "guitars".

(1) http://en.wikipedia.org/wiki/Keyboard_instrument
(2) http://de.wikipedia.org/wiki/Tasteninstrument