sdhci_fsl_fdt: Add voltage switching through syscon

Some SoCs does not have a fixed regulator to handle voltage
switching automatically. Add support for voltage switching
through syscon register when necessary. Add new errata flag
indicating missing regulator. Apply errata to SoCs, which are
known to be affected, i.e. LS1046 and LS1012.

Obtained from: Semihalf
Sponsored by: Alstom Group
Differential revision: https://reviews.freebsd.org/D34029