[ARM] 4807/2: ixp4xx: Merge nslu2-power.c into nslu2-setup.c

There is no reason to have power control in a separate file from the
board setup code.  Merge it back into the board setup file, removing
superfluous header includes and removing superfluous constants from
the machine header file.

--

Signed-off-by: Rod Whitby <rod@whitby.id.au>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>