arm/versatile: Add device tree support

For testing the dt work, define a dt-enabled versatile platform.

This patch adds a new versatile platform for when using the device
tree.  Add platform and amba devices are discovered and registered by
parsing the device tree.  Clocks and initial io mappings are still
configured statically.

This patch still depends on some static platform_data for a few devices
which is passed via the auxdata structure to of_platform_populate(),
but it is a viable starting point until the drivers can get all
configuration data out of the device tree.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>