soc: imx: add PM dependency for IMX7_PM_DOMAINS

soc: imx: add PM dependency for IMX7_PM_DOMAINS

The new pm domain driver causes a build failure when CONFIG_PM
is not set:

warning: (IMX7_PM_DOMAINS) selects PM_GENERIC_DOMAINS which has unmet direct dependencies (PM)
drivers/base/power/domain_governor.c: In function 'default_suspend_ok':
drivers/base/power/domain_governor.c:75:17: error: 'struct dev_pm_info' has no member named 'ignore_children'

This adds a dependency to ensure that we don't attempt to build the
driver without CONFIG_PM.

Fixes: 03aa12629fc4 ("soc: imx: Add GPCv2 power gating driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>