sepolicy: new prereboot_data_file type

This adds the type and permissions for dumping and appending prereboot
information.

Bug: 145203410
Test: Didn't see denials while dumping and appending prereboot info.
Change-Id: Ic08408b9bebc3648a7668ed8475f96a5302635fa
diff --git a/private/file_contexts b/private/file_contexts
index 0a0d3c9..8249d2a 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -540,6 +540,7 @@
 /data/misc/net(/.*)?            u:object_r:net_data_file:s0
 /data/misc/network_watchlist(/.*)? u:object_r:network_watchlist_data_file:s0
 /data/misc/perfetto-traces(/.*)? u:object_r:perfetto_traces_data_file:s0
+/data/misc/prereboot(/.*)?      u:object_r:prereboot_data_file:s0
 /data/misc/recovery(/.*)?       u:object_r:recovery_data_file:s0
 /data/misc/shared_relro(/.*)?   u:object_r:shared_relro_file:s0
 /data/misc/sms(/.*)?            u:object_r:radio_data_file:s0