DLL need only be enabled for speed modes and clock frequencies at or
above 50 MHz. For speed modes that don't enable the DLL, we need to
configure a static input delay value. This involves reading an optional
itap-del-sel-* value from the device tree and configuring it for the
appropriate speed mode.

With this addition, make sure that DLL is always switched off at the
beginning of the set_clock() call to simplify configuration. This also
removes the need for the dll_on member in struct sdhci_am654_data.
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Link: https://lore.kernel.org/r/20200923105206.7988-5-faiz_abbas@ti.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>