alpha: Fix de2104x driver failing to readout MAC address correctly

This patch fixes a missing read memory barrier that is needed for the
driver to readout the MAC address correctly from the on-board ROM.
Also it replaces the use of the deprecated functions readl()/writel().

Signed-off-by: Morten H. Larsen <m-larsen@post6.tele.dk>
Signed-off-by: Matt Turner <mattst88@gmail.com>