ramips: Power down phy on disabled switch ports

Power down phy on disabled switch ports.

Haven't measured this myself yet, but according to this
http://www.8devices.com/community/viewtopic.php?f=6&t=156


it can save about 300mW of power.

[juhosg: fix checkpatch warning]

Signed-off-by: Tobias Diedrich <ranma+openwrt@tdiedrich.de>

SVN-Revision: 33304