pmdomain: bcm: Move Kconfig options to the pmdomain subsystem

The Kconfig options belongs closer to the corresponding implementations,
hence let's move them from the soc subsystem to the pmdomain subsystem.

Cc: Florian Fainelli <florian.fainelli@broadcom.com>
Cc: Ray Jui <rjui@broadcom.com>
Cc: Scott Branden <sbranden@broadcom.com>
Cc: <linux-mips@vger.kernel.org>
Cc: <linux-rpi-kernel@lists.infradead.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>