- Add Gecko BURTC sys_clock driver to handle wake up from EM2,3 states
- Remove custom PM policy and dependency on HAL sl_power_manager service
- EM1 supported in all configurations
- EM2,3 supported only if SysTick is replaced by BURTC
Signed-off-by: Roman Dobrodii <rdobrodii@antmicro.com>