soc: Add SoC driver for Cirrus ep93xx

Add an SoC driver for the ep93xx. Currently there is only one thing
not fitting into any other framework, and that is the swlock setting.

Used for clock settings, pinctrl and restart.

Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>