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/zfs/zfs_dir.c

@@ -28,9 +28,7 @@
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/time.h>
-#include <sys/systm.h>
 #include <sys/sysmacros.h>
-#include <sys/resource.h>
 #include <sys/vfs.h>
 #include <sys/vnode.h>
 #include <sys/file.h>
@@ -41,7 +39,6 @@
 #include <sys/cmn_err.h>
 #include <sys/errno.h>
 #include <sys/stat.h>
-#include <sys/unistd.h>
 #include <sys/sunddi.h>
 #include <sys/random.h>
 #include <sys/policy.h>
@@ -49,7 +46,6 @@
 #include <sys/zfs_acl.h>
 #include <sys/zfs_vnops.h>
 #include <sys/fs/zfs.h>
-#include "fs/fs_subr.h"
 #include <sys/zap.h>
 #include <sys/dmu.h>
 #include <sys/atomic.h>
@@ -57,8 +53,6 @@
 #include <sys/zfs_fuid.h>
 #include <sys/sa.h>
 #include <sys/zfs_sa.h>
-#include <sys/dnlc.h>
-#include <sys/extdirent.h>
 
 /*
  * zfs_match_find() is used by zfs_dirent_lock() to peform zap lookups