Refactor zfs_context.h to build on FreeBSD

- on Linux move Linux specific headers to zfs_context_os.h
- on FreeBSD move FreeBSD specific definitions to zfs_context_os.h
- remove duplicate tsd_ definitions
- remove unused AT_TYPE

Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Don Brady <don.brady@delphix.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #9668

lib/libspl/include/sys/Makefile.am

@@ -4,7 +4,6 @@ libspldir = $(includedir)/libspl/sys
 libspl_HEADERS = \
 	$(top_srcdir)/lib/libspl/include/sys/acl.h \
 	$(top_srcdir)/lib/libspl/include/sys/acl_impl.h \
-	$(top_srcdir)/lib/libspl/include/sys/bitmap.h \
 	$(top_srcdir)/lib/libspl/include/sys/callb.h \
 	$(top_srcdir)/lib/libspl/include/sys/cmn_err.h \
 	$(top_srcdir)/lib/libspl/include/sys/cred.h \

lib/libspl/include/sys/bitmap.h

@@ -1,30 +0,0 @@
-/*
- * 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 2006 Sun Microsystems, Inc.  All rights reserved.
- * Use is subject to license terms.
- */
-
-#ifndef _LIBSPL_SYS_BITMAP_H
-#define	_LIBSPL_SYS_BITMAP_H
-
-#endif