dts: nxp_kinetis: Add spi bindings for kinetis dspi and update soc nodes

Adds dts spi bindings for the kinetis dspi controller, and updates the
k64, kw2xd, kw40z, kw41z dts nodes accordingly.

Updates the dts interrupt priorities to match the board defconfigs
(e.g., boards/arm/frdm_k64f/Kconfig.defconfig)

For k64, fixes an error in the spi1 interrupt number and adds a third
instance (spi2).

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