power: reset: at91-reset: add samx7 support

Add samx7 support. It is lacking a few bits and needs a new reset function.

Signed-off-by: Szemző András <sza@esh.hu>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>