irq_domain/powerpc: Replace custom xlate functions with library functions

This patch converts a number of the powerpc drivers to use the common library
of irq_domain xlate functions, dropping a bunch of lines in the process.

v5: - Remove tsi108 changes from patch

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Milton Miller <miltonm@bga.com>
Tested-by: Olof Johansson <olof@lixom.net>