ARM: at91/dt: sama5: update rstc to correct compatible string

They'll use "atmel,sama5d3-rstc" for reset function.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
[nicolas.ferre@atmel.com: add the old compatible string as a fallback]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>