arm: at91: dt: at91sam9 add serial pinctrl support

Set the dbgu pinctrl config by default as we have only one possible config
For other uart set the rxd/txd by default.

For at91sam9x5ek create soc based dts as we need to include specific soc dtsi.

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>