powerpc/fsl-booke: Add initial T4240QDS board support

Some minor changes to the common corenet_ds.c code are needed to support
the T4240QDS:
* Add support for "fsl,qoriq-pcie-v3.0" controller
* Bump max # of IRQs to 512 (T4240 supports more interrupts than
  previous SoCs).

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