Add linux kernel module support

Setup linux kernel module support, this includes:
- zfs context for kernel/user
- kernel module build system integration
- kernel module macros
- kernel module symbol export
- kernel module options

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/nvpair/nvpair_alloc_spl.c

@@ -0,0 +1,75 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License, Version 1.0 only
+ * (the "License").  You may not use this file except in compliance
+ * with the License.
+ *
+ * You can obtain a copy of the license at * usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#include <sys/nvpair.h>
+#include <sys/kmem.h>
+
+static void *
+nv_alloc_sleep_spl(nv_alloc_t *nva, size_t size)
+{
+	return (kmem_alloc(size, KM_SLEEP));
+}
+
+static void *
+nv_alloc_nosleep_spl(nv_alloc_t *nva, size_t size)
+{
+	return (kmem_alloc(size, KM_NOSLEEP));
+}
+
+static void
+nv_free_spl(nv_alloc_t *nva, void *buf, size_t size)
+{
+	kmem_free(buf, size);
+}
+
+const nv_alloc_ops_t spl_sleep_ops_def = {
+	NULL,                   /* nv_ao_init() */
+	NULL,                   /* nv_ao_fini() */
+	nv_alloc_sleep_spl,     /* nv_ao_alloc() */
+	nv_free_spl,            /* nv_ao_free() */
+	NULL                    /* nv_ao_reset() */
+};
+
+const nv_alloc_ops_t spl_nosleep_ops_def = {
+	NULL,                   /* nv_ao_init() */
+	NULL,                   /* nv_ao_fini() */
+	nv_alloc_nosleep_spl,   /* nv_ao_alloc() */
+	nv_free_spl,            /* nv_ao_free() */
+	NULL                    /* nv_ao_reset() */
+};
+
+nv_alloc_t nv_alloc_sleep_def = {
+	&spl_sleep_ops_def,
+	NULL
+};
+
+nv_alloc_t nv_alloc_nosleep_def = {
+	&spl_nosleep_ops_def,
+	NULL
+};
+
+nv_alloc_t *nv_alloc_sleep = &nv_alloc_sleep_def;
+nv_alloc_t *nv_alloc_nosleep = &nv_alloc_nosleep_def;