dts: arm: Kinetis: Add support for Hexiwear K64

This patch adds DTS support for the Hexiwear K64 platform.  This
includes enabling the DTS config option and adding conditionals around
the options to be replaced.

In addition, a DTS file is provided that customizes the Kinetis
platform to match the hexiwear board.  A fixup file is provided to map
the generated information to the current client driver usage.  This
file is temporary.

Change-Id: I247d538c6e13e0d1d4141fee74046575a7d2972e
Signed-off-by: Andy Gross <andy.gross@linaro.org>