tests: subsysm: pm: Enable power_mgmt_soc for MAX32690

This commit enables power_mgmt_soc test for MAX32690 board

Low power timer is used as idle timer that will wakeup device
from sleep modes. Lowpower timer clocked with RTC clock which
always on.

RTC can be used as idle clock timer too, in that case below
line need to be added in overlay file

/ {
    chosen {
    	zephyr,cortex-m-idle-timer = &rtc;
    };
};

&rtc {
    status = okay;
    wakeup-source;
};

Signed-off-by: Sadik Ozer <sadik.ozer@analog.com>