MFC r257393:

MFC r257393:

  Rework the imx ehci driver so that it's four separate ehci units rather
  than one unit with four busses attached to it.  This allows us to use
  existing fdt data which describes separate devices with separate resources.
  It also allows any combination of the units to be en/disabled in the
  board dts files.

  Adjust our dts code to match what's used by linux and u-boot now that
  we're structured to do so.

git-svn-id: svn://svn.freebsd.org/base/stable/10@259345 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f