Relax the sdhci(4) check that filters out the 1.8v voltage option unless
the slot is flagged as 'embedded'.

The features related to embedded and shared slots were added in v3.0 of
the sdhci spec. Hardware prior to v3 sometimes supported 1.8v on non-
removable devices in embedded systems, but had no way to indicate that
via the standard sdhci registers (instead they use out of band metadata
such as FDT data).

This change adds the controller specification version to the check for
whether to filter out the 1.8v selection. On older hardware, the 1.8v
option is allowed to remain. On 3.0 or later it still requires the
embedded-slot flag to remain.

This is part of the fix for PR 241301 (eMMC not detected on Beaglebone).
Changes to the sdhci_ti driver are also needed for a full fix.

PR: 241301