powerpc/85xx: Refactor P2041RDB to use common p_corenet files

The P2041RDB has almost identical setup for TLB, LAWS, and PCI with
other P-Series CoreNet platforms.

The only difference between P2041RDB & P3041DS/P4080DS/P5020DS is the
CPLD vs PIXIS FPGA which we can handle via some simple #ifdefs in the
TLB and LAW setup tables.

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