ARM: at91: Remove the old-style reset probing

Now that the reset code is a driver of its own, just let the usual DT probing
mecanism do its job, and remove the code entirely in this case.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>