[incremental] labels for incfs and directory root

Adding two labels: "incfs" for the incremental filesystem and
"incremental_root_file" for file paths /data/incremental/*.

Doc: go/incremental-selinux

Test: manual
Change-Id: I7d45ed1677e3422119b2861dfc7b541945fcb7a2
diff --git a/private/genfs_contexts b/private/genfs_contexts
index e33031a..5b956da 100644
--- a/private/genfs_contexts
+++ b/private/genfs_contexts
@@ -304,3 +304,4 @@
 genfscon usbfs / u:object_r:usbfs:s0
 genfscon binfmt_misc / u:object_r:binfmt_miscfs:s0
 genfscon bpf / u:object_r:fs_bpf:s0
+genfscon incremental-fs / u:object_r:incfs:s0