PM: Kconfig: fix unmet dependency for CPU_PM

If BL_SWITCHER is enabled but SUSPEND and CPU_IDLE is not enabled
we are getting following config warning.

warning: (BL_SWITCHER) selects CPU_PM which has unmet direct
dependencies (SUSPEND || CPU_IDLE)

It has been noticed that CPU_PM dependencies in this file are not really
required so let's remove these dependencies from CPU_PM.

Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>