sdhci_xenon: add UHS support

[mw]

Summary

This patch adds the necessary methods resolution to the sdhci_xenon
driver which are required to configure UHS modes for SD/MMC devices.
Apart from the two generic routines, the custom sdhci_xenon_set_uhs_timing
function is responsible for setting the SDHCI_HOST_CONTROL2 register
with appropriate mode select values - in case of HS200 and HS400
they are non-standard.

Test Plan

This is the end of entire series, HS200/HS400 and proper disabling of UHS via DT tested on:
MacchiatoBin
CN913x-DB
Marvell AC5x switch (CA55 with Xenon included)
Armada 8040 DB.