net: sun8i-emac: Drop use of arch-specific header

This header is not used since commit abdbefba ("net: sun8i_emac: Use
consistent clock bitfield definitions"). Dropping it allows the driver
to be architecture-independent.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>