FreeBSD: Do zcommon_init sooner to avoid FPU panic

There has been a panic affecting some system configurations where the
thread FPU context is disturbed during the fletcher 4 benchmarks,
leading to a panic at boot.

module_init() registers zcommon_init to run in the last subsystem
(SI_SUB_LAST).  Running it as soon as interrupts have been configured
(SI_SUB_INT_CONFIG_HOOKS) makes sure we have finished the benchmarks
before we start doing other things.

While it's not clear *how* the FPU context was being disturbed, this
does seem to avoid it.

Add a module_init_early() macro to run zcommon_init() at this earlier
point on FreeBSD.  On Linux this is defined as module_init().

Authored by: Konstantin Belousov <kib@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #11302

include/os/freebsd/spl/sys/mod_os.h

@@ -93,6 +93,13 @@ wrap_ ## fn(void *dummy __unused) \
 }																		\
 SYSINIT(zfs_ ## fn, SI_SUB_LAST, SI_ORDER_FIRST, wrap_ ## fn, NULL)
 
+#define	module_init_early(fn)							\
+static void \
+wrap_ ## fn(void *dummy __unused) \
+{								 \
+	fn();						 \
+}																		\
+SYSINIT(zfs_ ## fn, SI_SUB_INT_CONFIG_HOOKS, SI_ORDER_FIRST, wrap_ ## fn, NULL)
 
 #define	module_exit(fn) 							\
 static void \