Refactor sepolicy.rules resolve

We resolve available partitions for sepolicy.rules when patching
boot and bind mount the partition by magiskinit.

For older devices, the previous logic won't work because the part name
is never readable.

Co-authored-by: topjohnwu <topjohnwu@gmail.com>

scripts/avd_patch.sh

@@ -59,6 +59,8 @@ cp ramdisk.cpio ramdisk.cpio.orig
 
 touch config
 
+echo "RULESDEVICE=$(ISENCRYPTED=true ./magiskinit --rules-device)" >> config
+
 # For API 28, we also patch advancedFeatures.ini to disable SAR
 # Manually override skip_initramfs by setting RECOVERYMODE=true
 [ $API = "28" ] && echo 'RECOVERYMODE=true' >> config