arcnet: Remove function pointer macro indirections

It's clearer to use function pointer calls directly instead of the
macro indirections of ARCRESET, ACOMMAND, ASTATUS, and AINTMASK.

Remove the now unused macros too.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>