sepolicy: treat fuseblk as sdcard_external

Allow fuse-mounted NTFS/exFAT file systems to be written to

Change-Id: I1492914dd269a305e27aba58e61064d853adf2bc
diff --git a/sepolicy/genfs_contexts b/sepolicy/genfs_contexts
new file mode 100644
index 0000000..cec9f01
--- /dev/null
+++ b/sepolicy/genfs_contexts
@@ -0,0 +1 @@
+genfscon fuseblk / u:object_r:sdcard_external:s0