powerpc/windfarm: Add detection for second cpu pump

Windfarm SMU control is explicitly missing support for a second CPU pump in G5 PowerMacs. Such machines actually exist  (specifically Quads with a second pump), so this patch adds detection for it.

Signed-off by: Bolko Maass <bmaass@math.uni-bremen.de>
CC: <stable@kernel.org>

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>