power: fix Kconfig defaults

Some SoCs try to select power management in a way that can bypass the
dependency on system clock.  Make the selection conditional on the
dependency.

Signed-off-by: Peter Bigot <[email protected]>

Author: pabigot

soc/arm/microchip_mec/mec1501/Kconfig.defconfig.mec1501hsz

@@ -62,7 +62,7 @@ config SPI_XEC_QMSPI
 if SOC_POWER_MANAGEMENT
 
 config PM
-	default y
+	default y if SYS_CLOCK_EXISTS
 
 config PM_SLEEP_STATES
 	default y

soc/arm/nordic_nrf/Kconfig.defconfig

@@ -28,7 +28,7 @@ config ARCH_HAS_CUSTOM_BUSY_WAIT
 	default y
 
 config PM
-	default y
+	default y if SYS_CLOCK_EXISTS
 
 config BUILD_OUTPUT_HEX
 	default y