Use Toradex layers for Toradex boards

The Toradex layers have newer kernel versions and U-Boot compared to meta-freescale-3rdparty. Note also that meta-toradex has been split up to smaller, pure BSP layers. To support the NXP based boards, the two layers meta-toradex-bsp-common and meta-toradex-nxp should be sufficient.

This also contains support for the Toradex Easy Installer image format. This installer will be preinstalled on modules modules soon. Providing Boot2Qt images in the Installer Format would make it really easy for customers to flash Boot2Qt to the internal eMMC.