module/*.ko: prune .data, global .rodata

Evaluated every variable that lives in .data (and globals in .rodata)
in the kernel modules, and constified/eliminated/localised them
appropriately. This means that all read-only data is now actually
read-only data, and, if possible, at file scope. A lot of previously-
global-symbols became inlinable (and inlined!) constants. Probably
not in a big Wowee Performance Moment, but hey.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12899

module/zfs/spa_config.c

@@ -68,7 +68,9 @@ static uint64_t spa_config_generation = 1;
  * userland pools when doing testing.
  */
 char *spa_config_path = ZPOOL_CACHE;
-int zfs_autoimport_disable = 1;
+#ifdef _KERNEL
+static int zfs_autoimport_disable = B_TRUE;
+#endif
 
 /*
  * Called when the module is first loaded, this routine loads the configuration