[POWERPC] mpc5200: Add generic support for simple MPC5200 based boards

[POWERPC] mpc5200: Add generic support for simple MPC5200 based boards

This patch adds support for 'mpc5200-simple-platform' compatible
boards which do not need a platform specific setup. Such boards
are supported assuming the following:

- GPIO pins are configured by the firmware,
- CDM configuration (clocking) is setup correctly by firmware,
- if the 'fsl,has-wdt' property is present in one of the
  gpt nodes, then it is safe to use such gpt to reset the board,
- PCI is supported if enabled in the kernel configuration
  and if there is a PCI bus node defined in the device tree.

Signed-off-by: Marian Balakowicz <m8@semihalf.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>