Define contextmount_type attribute and add it to oemfs.

Several device-specific policy changes with the same Change-Id
also add this attribute to device-specific types.

Change-Id: I09e13839b1956f61875a38844fe4fc3c911ea60f
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

attributes

@@ -11,6 +11,9 @@ attribute domain;
 # All types used for filesystems.
 attribute fs_type;
 
+# All types used for context= mounts.
+attribute contextmount_type;
+
 # All types used for files that can exist on a labeled fs.
 # Do not use for pseudo file types.
 attribute file_type;

file.te

@@ -33,7 +33,7 @@ type sdcard_external, sdcard_type, fs_type, mlstrustedobject;
 type debugfs, fs_type, mlstrustedobject;
 type pstorefs, fs_type;
 type functionfs, fs_type;
-type oemfs, fs_type;
+type oemfs, fs_type, contextmount_type;
 type usbfs, fs_type;
 
 # File types