can: mscan: mpc5xxx_can: Prepare cleanup of powerpc's asm/prom.h

powerpc's asm/prom.h brings some headers that it doesn't need itself.

In order to clean it up, first add missing headers in users of
asm/prom.h

Link: https://lore.kernel.org/all/878888f9057ad2f66ca0621a0007472bf57f3e3d.1648833432.git.christophe.leroy@csgroup.eu


Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>