Convert the binding to DT schema format. Also update the binding
to fix shortcomings

 * Add "nxp,kinetis-k20" fallback compatible
 * add programming SPI interface and reset GPIO
 * add main clock
 * add voltage supplies
 * drop spi-max-frequency from required properties,
   driver will setup max. frequency
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20210802172309.164365-2-sebastian.reichel@collabora.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>