ARM: bcm283x: use OF_CONTROL for bcm283x

This patch removes use of U_BOOT_DEVICE in board/raspberrypi/rpi/rpi.c,
enables OF_CONTROL in the config and adjusts the rpi_*defconfig configs.

Signed-off-by: Fabian Vogt <fvogt@suse.com>
Reviewed-by: Simon Glass <sjg@chromium.org>