ARM: OMAP: convert omap_device_build() and callers to __init

Building omap_devices should only be done at init time, and since
omap_device_build() is using early_platform calls which are also
__init, this ensures that omap_device isn't trying to use functions
that disappear.

Signed-off-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>