ARM: at91: Remove reset code from the machine code

Now that the transition is over and that we probe our reset driver in every
case, we can remove the legacy code from the machine directory.

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>