Add msec/usec/nsec to tick convertors

Add wrappers for the Solaris MSEC_TO_TICK, USEC_TO_TICK, and
NSEC_TO_TICK conversion functions.  They are mapped directly to
their Linux counterparts with the exception of NSEC_TO_TICK
can cannot use usecs_to_jiffies() because it is not exported
by the kernel.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Fix delay()

Somewhat amazingly it went unnoticed that the delay() function
doesn't actually cause the task to block.  Since the task state
is never changed from TASK_RUNNING before schedule_timeout() the
scheduler allows to task to continue running without any delay.
Using schedule_timeout_interruptible() resolves the issue by
correctly setting TASK_UNINTERRUPTIBLE.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>