omap-mcbsp: added (optional) tristate facility through pinctrl

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
GTA04 DT: defined pinmux for all McBSPs and made McBSP4 with tristate option

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Pyra DT: fixed a typo

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
GTA04 sound: perpared for the new tristate facility

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>