classes/use-imx-headers: Easy linux-imx-headers use

classes/use-imx-headers: Easy linux-imx-headers use

This allow to easy reuse of binary packages among similar SoCs. The
usual use for this is to share SoC specific packages among different
boards independently of the kernel version it is using, as far it is
ABI compatible with the official version it will just work.

Following recipes has been reworked to make use of the class:

 - imx-lib
 - imx-test
 - imx-vpu-hantro
 - imx-vpu
 - imx-alsa-plugins
 - gstreamer1.0-plugins-base
 - gstreamer1.0-plugins-imx
 - imx-gst1.0-plugin

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Tom Hochstein <tom.hochstein@nxp.com>