macb: Fix build with macro'ized readl/writel.

If an architecture defines readl/writel using CPP macros, we
get the following kinds of build failure:

> > > drivers/net/ethernet/cadence/macb.c:164:1: error: macro "writel"
> > > passed 3 arguments, but takes just 2
>      macb_or_gem_writel(bp, SA1B, bottom);
>     ^

Rename the methods so that this doesn't happen.

Signed-off-by: David S. Miller <davem@davemloft.net>