Revert "dm: arm: rpi: Drop CONFIG_OF_EMBED"

This reverts commit 25877d4e.

This is a workaround for Raspberry Pi boot failures seen when passing on
the device tree provided by the Raspberry Pi firmware at boot. Without
CONFIG_OF_EMBED, we just get stuck at "Starting kernel ..." when we try
to boot Linux with this device tree.

Signed-off-by: Paul Barker <pbarker@toganlabs.com>
Cc: Simon Glass <sjg@chromium.org>
Tested-by: Jonathan Gray <jsg@jsg.id.au>
Reviewed-by: Simon Glass <sjg@chromium.org>