p4dpe/g2 committed

[Ronald G. Minnich]

I have just commited the p4dpe-g2 variant of the p4dpe, structured as
src/mainboard/supermicro/p4dpe/g2

I have built and tested this technique and it works fine for both fallback 
and normal modes, and two sample .config files are included in the 
directory. 

So we now have a standard way to handle mainboard variants. Both the 
mptable and irq_table had to change for the -g2

ron