On my splitkb_aurora_lily58 the rgb would not come on after a pm_soft_off. The issue was twofold:

• CONFIG_ZMK_RGB_UNDERGLOW_EXT_POWER is set to y by default, so the rgb state controls the ext_power state. ext_power should not manage its own state in that case.
• ext_power state changes due to pm actions should not affect the stored ext_power state, only user invoked changes should, otherwise a pm_soft_off will permanently switch off rgb eventhough it was switched on before the shutdown.

This PR fixes both these issues.