net: sun8i_emac: Wrap and simplify cache maintenance operations

To meet the current alignment requirements for our cache maintenance
functions, we were explicitly aligning the *arguments* to those calls.
This is not only ugly to read, but also wrong, as we need to make sure
we are not accidentally stepping on other data.

Provide wrapper functions for the common case of cleaning or
invalidating a descriptor, to make the cache maintenance calls more
readable. This fixes a good deal of the problematic calls.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Amit Singh Tomar <amittomer25@gmail.com> # Pine64+
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>