net: stmmac: add support for dwmac 3.40a

[ Upstream commit 9cb1d19f47fafad7dcf7c8564e633440c946cfd7 ]

dwmac 3.40a is an old ip version that can be found on SPEAr3xx soc.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>