boards: dts: Add mcr20a bindings and fix networking samples

Adds dts bindings for the mcr20a wireless transceiver. The frdm_k64f
board supports the mcr20a via an Arduino shield, therefore the dts node
is added to the board dts. The kw2xd is a SiP and thus the mcr20a dts
node is added to the soc dts.

The networking samples using prj_frdm_k64f_mcr20a.conf have been broken
since the refactoring of the mcux gpio driver to dts in commit
4e8f29f3. The sample is now fixed.

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