power: reset: Add a driver for the ep93xx reset

Implement the reset behaviour of the various EP93xx SoCS
in drivers/power/reset.

It used to be located in arch/arm/mach-ep93xx.

Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Acked-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>