Revert "of: use platform_device_add"

This reverts commit aac73f34. That
commit causes two kinds of breakage; it breaks registration of AMBA
devices when one of the parent nodes already contains overlapping
resource regions, and it breaks calls to request_region() by device
drivers in certain conditions where there are overlapping memory
regions. Both of these problems can probably be fixed, but it is better
to back out the commit and get a proper fix designed before trying again.

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