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/arc.c

@@ -292,11 +292,9 @@
 #include <sys/zil.h>
 #include <sys/fm/fs/zfs.h>
 #ifdef _KERNEL
+#include <sys/shrinker.h>
 #include <sys/vmsystm.h>
-#include <vm/anon.h>
-#include <sys/fs/swapnode.h>
 #include <sys/zpl.h>
-#include <linux/mm_compat.h>
 #include <linux/page_compat.h>
 #endif
 #include <sys/callb.h>
@@ -1199,7 +1197,7 @@ buf_fini(void)
 {
 	int i;
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 	/*
 	 * Large allocations which do not require contiguous pages
 	 * should be using vmem_free() in the linux kernel\
@@ -1360,7 +1358,7 @@ buf_init(void)
 		hsize <<= 1;
 retry:
 	buf_hash_table.ht_mask = hsize - 1;
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 	/*
 	 * Large allocations which do not require contiguous pages
 	 * should be using vmem_alloc() in the linux kernel
@@ -9050,7 +9048,7 @@ l2arc_stop(void)
 	mutex_exit(&l2arc_feed_thr_lock);
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 EXPORT_SYMBOL(arc_buf_size);
 EXPORT_SYMBOL(arc_write);
 EXPORT_SYMBOL(arc_read);