linux: module: weld all but spl.ko into zfs.ko

Originally it was thought it would be useful to split up the kmods
by functionality.  This would allow external consumers to only load
what was needed.  However, in practice we've never had a case where
this functionality would be needed, and conversely managing multiple
kmods can be awkward.  Therefore, this change merges all but the
spl.ko kmod in to a single zfs.ko kmod.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13274

module/zstd/zfs_zstd.c

@@ -702,7 +702,7 @@ zstd_meminit(void)
 }
 
 /* Release object from pool and free memory */
-static void __exit
+static void
 release_pool(struct zstd_pool *pool)
 {
 	mutex_destroy(&pool->barrier);
@@ -712,7 +712,7 @@ release_pool(struct zstd_pool *pool)
 }
 
 /* Release memory pool objects */
-static void __exit
+static void
 zstd_mempool_deinit(void)
 {
 	for (int i = 0; i < ZSTD_POOL_MAX; i++) {
@@ -758,7 +758,7 @@ zstd_init(void)
 	return (0);
 }
 
-extern void __exit
+extern void
 zstd_fini(void)
 {
 	/* Deinitialize kstat */
@@ -776,12 +776,10 @@ zstd_fini(void)
 }
 
 #if defined(_KERNEL)
+#ifdef __FreeBSD__
 module_init(zstd_init);
 module_exit(zstd_fini);
-
-ZFS_MODULE_DESCRIPTION("ZSTD Compression for ZFS");
-ZFS_MODULE_LICENSE("Dual BSD/GPL");
-ZFS_MODULE_VERSION(ZSTD_VERSION_STRING "a");
+#endif
 
 EXPORT_SYMBOL(zfs_zstd_compress);
 EXPORT_SYMBOL(zfs_zstd_decompress_level);