powerpc/85xx: refactor common P-Series CoreNet files for FSL boards

We currently support 4 SoC/Boards from the P-Series of QorIQ SoCs that
are based on the 'CoreNet' Architecture: P2041RDB, P3041DS, P4080DS, and
P5020DS.  There is a significant amount of commonality shared between
these boards that we can refactor into common code:

* Initial LAW setup
* Initial TLB setup
* PCI setup

We start by moving the shared code between P3041DS, P4080DS, and P5020DS
into a common directory to be shared with other P-Series CoreNet boards.

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