boards: hexiwear_k64f: Default to jlink firmware and jlink runner

The hexiwear_k64f and hexiwear_kw40z share the same OpenSDA
microcontroller on the hexiwear docking station, so make the jlink the
default firmware on both for consistency. We use jlink instead of
daplink by default because hexiwear_kw40z can only use Segger RTT for
the console (there is no UART available).

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>