[POWERPC] Reduce code duplication in legacy_serial, add UART parent types

The legacy_serial was treating each UART parent in a separate code block.
Rather than continue this trend for the new parent IDs, this condenses
all (soc, tsi, opb, plus two more new types) into one of_device_id array.
The new types are wrs,epld-localbus for the Wind River sbc8560, and a
more generic "simple-bus" as requested by Scott Wood.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>