i8k: make fan multiplier tunable with a module parameter

The i8k driver multiplies the fan speed reported by the BIOS with a factor of
30.  On my Dell Latitude D800, this factor is not required.

I'd suggest to make this configurable.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>