Add interface to read efivarfs_t directory

I'm seeing the following denial when using 'efivars --list'.  This
interface grants access
2019-12-17T15:22:06-05:00 ip-tsc-black tag_audit_log: type=AVC msg=audit(1576596109.149:95): avc:  denied  { read } for  pid=2329 comm="efivar" name="/" dev="efivarfs" ino=11266 scontext=system_u:system_r:my_app_t:s0 tcontext=system_u:object_r:efivarfs_t:s0 tclass=dir permissive=1

Signed-off-by: Dave Sugar <dsugar@tresys.com>

policy/modules/kernel/filesystem.if

@@ -1982,6 +1982,24 @@ interface(`fs_manage_dos_files',`
 	manage_files_pattern($1, dosfs_t, dosfs_t)
 ')
 
+########################################
+## <summary>
+##	List dirs in efivarfs filesystem.
+## </summary>
+## <param name="domain">
+##	<summary>
+##	Domain allowed access.
+##	</summary>
+## </param>
+#
+interface(`fs_list_efivars',`
+	gen_require(`
+		type efivarfs_t;
+	')
+
+	list_dirs_pattern($1, efivarfs_t, efivarfs_t)
+')
+
 #######################################
 ## <summary>
 ##      Read files in efivarfs