ARM: at91/dt: sama5d4: add uart0, uart1 dt nodes

Add sama5d4 uart0, uart1 dt nodes, pinctrl and related aliases.

Signed-off-by: Suchang Ko <suchangko@samul.kr>
[nicolas.ferre@atmel.com: split patch, reorder & whitespace fixes]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>