mmc: sdhci-xenon: switch to device_* API

In order to support both ACPI and DT, modify the driver
to use device_* routines for obtaining the properties
values.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Link: https://lore.kernel.org/r/20201204171626.10935-3-mw@semihalf.com


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