ARM: kirkwood: Trim excess #includes in board-dnskw.c

Lots of code has now moved into the devicetree, leaving a collection of
useless header files. Tidy them up.

This applies cleanly atop of my previous patch, "[PATCH V2 2/2] ARM:
kirkwood: Use devicetree to define DNS-32[05] fan", which also removes
gpio-fan.h

Signed-off-by: Jamie Lentin <jm@lentin.co.uk>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>