Is DDR_SEL in IOMUXC_SW_PAD_CTL_GRP_DDR_TYPE_RGMII set to b11 in u-boot for Sabre SD, since NVCC_RGMII is 1.5V? Or is it left at the default b10 (1.2V)?
For DSE in IOMUXC_SW_PAD_CTL_PAD_RGMII_RXC, the default is b110. This is 37 ohms, too low for most boards. Is it set anywhere in u-boot?
I did a grep for IOMUXC_SW_PAD_CTL_GRP_DDR_TYPE_RGMII and IOMUXC_SW_PAD_CTL_PAD_RGMII_RXC and found nothing.