tests: pm: power_mgmt_soc: enable testing on twr_ke18f

Enable the SoC power management test suite on the NXP TWR-KE18F
development board.

Signed-off-by: Henrik Brix Andersen <[email protected]>

Author: henrikbrixandersen

tests/subsys/pm/power_mgmt_soc/testcase.yaml

@@ -1,5 +1,5 @@
 tests:
   subsys.pm.pm_soc:
     platform_allow: cc26x2r1_launchxl cc1352r1_launchxl mec15xxevb_assy6853 mec1501modular_assy6885
-       nucleo_wb55rg nucleo_l476rg
+       nucleo_wb55rg nucleo_l476rg twr_ke18f
     tags: power