Wrap smp_processor_id in kpreempt_[dis|en]able

After surveying the code, the few places where smp_processor_id is used
were deemed to be safe to use with a preempt enabled kernel. As such, no
core logic had to be changed. These smp_processor_id call sites are simply
are wrapped in kpreempt_disable and kpreempt_enabled to prevent the
Linux kernel from emitting scary warnings.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Issue #83

include/sys/zfs_context.h

@@ -61,6 +61,7 @@
 #include <sys/fm/fs/zfs.h>
 #include <sys/sunddi.h>
 #include <sys/ctype.h>
+#include <sys/disp.h>
 #include <linux/dcache_compat.h>
 
 #else /* _KERNEL */
@@ -228,6 +229,9 @@ extern kthread_t *zk_thread_create(caddr_t stk, size_t  stksize,
 	proc_t *pp, int state, pri_t pri);
 extern void zk_thread_join(kt_did_t tid);
 
+#define	kpreempt_disable()	((void)0)
+#define	kpreempt_enable()	((void)0)
+
 #define	PS_NONE		-1
 
 #define	issig(why)	(FALSE)