mmc: sdhci_am654: Enable DLL only for some speed modes

Its recommended that DLL must only be enabled for SDR50, DDR50, DDR52,
SDR104, HS200 and HS400 speed modes. Move DLL configuration to its own
function and call it only in the above speed modes.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20200108150920.14547-4-faiz_abbas@ti.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>