ARM: dts: at91: sam9x60: Add missing pinctrl node properties

Add the missing properties for the pinctrl node and for its
corresponding GPIO bank nodes to align with the Linux DT.

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
Reviewed-by: Eugen Hristev <eugen.hristev@linaro.org>