[U-Boot] ARM LED weak symbols

[Tom Rix]

As discussed earlier today

http://lists.denx.de/pipermail/u-boot/2009-November/063711.html

This is the patch to conditionally compile the ARM board LED
functions.

It was regression tested with MAKEALL arm using the 
Code Sourcery 2009 compiler and my roll-your-own gcc-4.4.2

Both patches were runtested with the Code Sourcery compiler on Zoom2.

Since this is a common patch, I would like to see it
tested on other boards (hint).  

I will wait till tomorrow for comments and then push it
to arm/next.

Tom