net: dsa: qca8k: Enable delay for RGMII_ID mode

RGMII_ID specifies that we should have internal delay, so resurrect the
delay addition routine but under the RGMII_ID mode.

Fixes: 40269aa9f40a ("net: dsa: qca8k: disable delay for RGMII mode")
Tested-by: Michal Vokáč <michal.vokac@ysoft.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>