net: sun8i-emac: Use common syscon setup for R40

net: sun8i-emac: Use common syscon setup for R40

While R40 puts the EMAC syscon register at a different address from
other variants, the relevant portion of the register's layout is the
same. Factor out the register offset so the same code can be shared
by all variants. This matches what the Linux driver does.

This change provides two benefits beyond the simplification:
 - R40 boards now respect the RX delays from the devicetree
 - This resolves a warning on architectures where readl/writel
   expect the address to have a pointer type, not phys_addr_t.

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