MFC r281073, r281074, r281077, r281200:

MFC r281073, r281074, r281077, r281200:

  Use OF_getencprop over OF_getprop and fdt32_to_cpu. The latter may give
  us the wrong data in the failure case if shift was not zero.

  Remove the extra copy of uart_fdt_get_clock and uart_fdt_get_shift. While
  here also use OF_getencprop in uart_fdt_get_clock.

  Move uart_fdt_get_clock and uart_fdt_get_shift to uart_bus_fdt.c, we may
  not build uart_cpu_fdt.c in all configs.

  Fix uart_fdt_get_clock. It should have been using the cell variable passed
  in, not value on the stack.

git-svn-id: svn://svn.freebsd.org/base/stable/10@283481 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f