NFS: add missing spkm3 strings to mount option parser

This patch adds previous missing spkm3 string values that are needed
to parse mount options in the kernel.
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 7f4505f..1fb3818 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -190,6 +190,10 @@
 	{ Opt_sec_lkeyi, "lkeyi" },
 	{ Opt_sec_lkeyp, "lkeyp" },
 
+	{ Opt_sec_spkm, "spkm3" },
+	{ Opt_sec_spkmi, "spkm3i" },
+	{ Opt_sec_spkmp, "spkm3p" },
+
 	{ Opt_sec_err, NULL }
 };