ARM: at91/dt: add pinctrl definition for at91 tc blocks

This patch adds pinctrl configurations for at91 Timer Counter blocks.
These pin definitions can be referenced by "atmel,tcb-pwm" devices to
setup pins as PWM output for instance.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
[nicolas.ferre@atmel.com: switch to pinctrl pre-processor macros]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>