Add sdcardfs variable to storage_config_props

This property allows us to disable sdcardfs if it is present. The old
property ended up getting repurposed, so a new one was needed.
Mediaprovider will also need to access this to determine what actions it
needs to take.

Test: builds
Bug: 155222498
Change-Id: I66ac106613cbb374f54659601e4ba3f61eaecd2f
diff --git a/private/property_contexts b/private/property_contexts
index cfcfd5e..326c474 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -416,6 +416,7 @@
 
 external_storage.projid.enabled   u:object_r:storage_config_prop:s0 exact bool
 external_storage.casefold.enabled u:object_r:storage_config_prop:s0 exact bool
+external_storage.sdcardfs.enabled u:object_r:storage_config_prop:s0 exact bool
 
 ro.enable_boot_charger_mode u:object_r:exported3_default_prop:s0 exact bool