mmcbr_retune
err = mmcbr_retune(busdev, reset);
DEVMETHOD(mmcbr_retune, rtsx_mmcbr_retune),
DEVMETHOD(mmcbr_retune, sdhci_generic_retune),
DEVMETHOD(mmcbr_retune, sdhci_fsl_fdt_retune),
DEVMETHOD(mmcbr_retune, sdhci_generic_retune),
DEVMETHOD(mmcbr_retune, sdhci_generic_retune),