charger: Add API to replace ro.charger.enable_suspend

The system property is set by vendor partition but owned by platform,
hence vendor domains can't read this value. Add an API in
ChargerConfigurationInterface so that HAL implementations can override
its value.

Other ro.charger.* sysprops are unused, hence no APIs are created for
them.

Test: manual
Bug: 203246116

Change-Id: I583c21e58ed3d912b156e253d6a4b46a0378f11e