powerpc/p5020: Add various p5020 related defines (and p5010)

There are various locations that we have chip specific info:

* Makefile for which ddr code to build
* Added p5020 & p5010 to cpu_type_list and SVR list
* Added number of LAWs for p5020
* Set CONFIG_MAX_CPUS to 2 for p5020

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>