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/lua/lapi.c

@@ -1279,7 +1279,7 @@ LUA_API void lua_upvaluejoin (lua_State *L, int fidx1, int n1,
   luaC_objbarrier(L, f1, *up2);
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 
 static int __init
 lua_init(void)

module/lua/lauxlib.c

@@ -788,7 +788,7 @@ LUALIB_API void luaL_checkversion_ (lua_State *L, lua_Number ver) {
   lua_pop(L, 1);
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 
 EXPORT_SYMBOL(luaL_argerror);
 EXPORT_SYMBOL(luaL_error);

module/lua/lbaselib.c

@@ -288,7 +288,7 @@ LUAMOD_API int luaopen_base (lua_State *L) {
   return 1;
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 
 EXPORT_SYMBOL(luaopen_base);
 

module/lua/lcorolib.c

@@ -151,7 +151,7 @@ LUAMOD_API int luaopen_coroutine (lua_State *L) {
   return 1;
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 
 EXPORT_SYMBOL(luaopen_coroutine);
 

module/lua/lstrlib.c

@@ -1032,7 +1032,7 @@ LUAMOD_API int luaopen_string (lua_State *L) {
   return 1;
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 
 EXPORT_SYMBOL(luaopen_string);
 

module/lua/ltablib.c

@@ -281,7 +281,7 @@ LUAMOD_API int luaopen_table (lua_State *L) {
   return 1;
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 
 EXPORT_SYMBOL(luaopen_table);