Update build system and packaging

Minimal changes required to integrate the SPL sources in to the
ZFS repository build infrastructure and packaging.

Build system and packaging:
  * Renamed SPL_* autoconf m4 macros to ZFS_*.
  * Removed redundant SPL_* autoconf m4 macros.
  * Updated the RPM spec files to remove SPL package dependency.
  * The zfs package obsoletes the spl package, and the zfs-kmod
    package obsoletes the spl-kmod package.
  * The zfs-kmod-devel* packages were updated to add compatibility
    symlinks under /usr/src/spl-x.y.z until all dependent packages
    can be updated.  They will be removed in a future release.
  * Updated copy-builtin script for in-kernel builds.
  * Updated DKMS package to include the spl.ko.
  * Updated stale AUTHORS file to include all contributors.
  * Updated stale COPYRIGHT and included the SPL as an exception.
  * Renamed README.markdown to README.md
  * Renamed OPENSOLARIS.LICENSE to LICENSE.
  * Renamed DISCLAIMER to NOTICE.

Required code changes:
  * Removed redundant HAVE_SPL macro.
  * Removed _BOOT from nvpairs since it doesn't apply for Linux.
  * Initial header cleanup (removal of empty headers, refactoring).
  * Remove SPL repository clone/build from zimport.sh.
  * Use of DEFINE_RATELIMIT_STATE and DEFINE_SPINLOCK removed due
    to build issues when forcing C99 compilation.
  * Replaced legacy ACCESS_ONCE with READ_ONCE.
  * Include needed headers for `current` and `EXPORT_SYMBOL`.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
TEST_ZIMPORT_SKIP="yes"
Closes #7556

module/icp/algs/skein/skein.c

@@ -7,8 +7,8 @@
 
 #define	SKEIN_PORT_CODE		/* instantiate any code in skein_port.h */
 
+#include <sys/sysmacros.h>
 #include <sys/types.h>
-#include <sys/note.h>
 #include <sys/skein.h>		/* get the Skein API definitions   */
 #include "skein_impl.h"		/* get internal definitions */
 

module/icp/algs/skein/skein_impl.h

@@ -25,16 +25,11 @@
 #define	_SKEIN_IMPL_H_
 
 #include <sys/skein.h>
+#include <sys/strings.h>
+#include <sys/note.h>
 #include "skein_impl.h"
 #include "skein_port.h"
 
-/* determine where we can get bcopy/bzero declarations */
-#ifdef	_KERNEL
-#include <sys/systm.h>
-#else
-#include <strings.h>
-#endif
-
 /*
  * "Internal" Skein definitions
  *    -- not needed for sequential hashing API, but will be

module/icp/algs/skein/skein_port.h

@@ -16,7 +16,6 @@
 #define	_SKEIN_PORT_H_
 
 #include <sys/types.h>	/* get integer type definitions */
-#include <sys/systm.h>	/* for bcopy() */
 
 #ifndef	RotL_64
 #define	RotL_64(x, N)	(((x) << (N)) | ((x) >> (64 - (N))))