pmdomain: imx: Move Kconfig options to the pmdomain subsystem

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

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: <kernel@pengutronix.de>
Cc: <linux-imx@nxp.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>