Simplify and make consistent the current uses of readb/writeb
by using the newly introduced arcnet_<I/O> equivalents.

o Add new #defines for register offsets
o Remove old #defines that included the ioaddr
o Remove obfuscating macros by expanding them in-place where appropriate
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>