MFC r257518, r257519:

MFC r257518, r257519:

  TI sdhci driver improvements, mostly related to fdt data...

  Use the published compatible strings (our own invention, "ti,mmchs" is
  still accepted as well, for now).

  Don't blindly turn on 8-bit bus mode, because even though the controller
  supports it, the board has to be wired appropriately as well.  Use the
  published property (bus-width=<n>) and honor all the valid values (1,4,8).

  The eMMC device on a Beaglebone Black is wired for 8-bit, update the dts.

  The mmchs controller can inherently do both 1.8v and 3.0v on the first
  device and 1.8v only on other devices, unless an external transceiver is
  used.  Set the voltage automatically for the first device and honor
  the published fdt property (ti,dualvolt) for other devices.

git-svn-id: svn://svn.freebsd.org/base/stable/10@259356 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f