apexd_prop is defined for PRODUCT_COMPATIBLE_PROPERTY = false case

apexd_prop is also defined in private/propery_contexts in order to make
the type to exist even when PRODUCT_COMPATIBLE_PROPERTY is false (i.e.,
Pixel 1).

Bug: 119220815
Test: m plat_property_contexts for sailfish
the built plat_property_contexts has apexd_prop defined

Change-Id: I9ef71410533c1f64fc6a3112cfcb199d23aaf3db

private/property_contexts

@@ -164,3 +164,5 @@ persist.time.           u:object_r:time_prop:s0
 
 # Properties that relate to server configurable flags
 persist.device_config.attempted_boot_count        u:object_r:device_config_boot_count_prop:s0
+
+apexd.                  u:object_r:apexd_prop:s0