header: add of_platform_populate()

of_platform_populate() is not added when CONFIG_OF_DEVICE is not set on
kernel < 3.4.
The same is true for of_default_bus_match_table on kernel < 3.11. we do
not need to provide a real implementation of of_default_bus_match_table
because it will be accessed.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>