drivers: remove unnecessary prom.h includes

Remove unnecessary prom.h includes in preparation to remove implicit
includes of prom.h.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>
Acked-by: Grant Likely <grant.likely@linaro.org>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Cc: linux-can@vger.kernel.org
Cc: netdev@vger.kernel.org