drivers: display: Introduce mcux elcdif shim driver

Adds a shim layer around the mcux elcdif driver to adapt it to the
zephyr display interface. Although the hardware and underlying mcux sdk
driver can support additional configurations, some shortcuts are
currently made in the shim that force a given pixel format, lcd data
bus width, and signal polarity. This works with the rocktech lcd module
used on imx rt boards, but will need to be updated for other display
panels.

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