ARM: at91: Add at91sam9rl DT SoC support

This adds preliminary DT support for the at91sam9rl.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Boris BREZILLON <b.brezillon.dev@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>