From: Ingo Molnar <mingo@elte.hu>

We have various different implementations of MSEC[S]_TO_JIFFIES and
JIFFIES_TO_MSEC[S].  We recently had a compile-time clash in USB.

Fix all that up.

- The SCTP version was very inefficient.  Hopefully this version is accurate
  enough.

- Optimise for the HZ=100 and HZ=1000 cases

- This version does round-up, so sleep(9 milliseconds) works OK on 100HZ.

- We still have lots of jiffies_to_msec and msec_to_jiffies implementations.

From: William Lee Irwin III <wli@holomorphy.com>

  Optimize the cases where HZ is a divisor of 1000 or vice-versa in
  JIFFIES_TO_MSECS() and MSECS_TO_JIFFIES() by allowing the nonvanishing(!)
  integral ratios to appear as a parenthesized expressions eligible for
  constant folding optimizations.

From: me

  Use typesafe inlines for the jiffies-to-millisecond conversion functions.

  This means that milliseconds officially takes the type `unsigned int'.
  All current callers seem to be OK with that.

  Drivers need to be fixed up to use this instead of their private versions.