Allow charger to read ro.charger.*

Allow charger to read system properties with this prefix
so that charger's behavior is controlled by runtime.

Test: run offline charging on walleye
Bug: 124118169
Change-Id: I4266b2d043a5323b4adbd1636ada46b7e08ca667
diff --git a/private/property_contexts b/private/property_contexts
index 520383d..9df2608 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -206,3 +206,6 @@
 
 # Property that is set once ueventd finishes cold boot.
 ro.cold_boot_done       u:object_r:cold_boot_done_prop:s0
+
+# Charger properties
+ro.charger.             u:object_r:charger_prop:s0