reproduce (this is a W=1 build):
        # https://github.com/Freescale/linux-fslc/commit/49e0afc879aa92d4c9ff99b7b92a6ee5d4ba127b
        git remote add freescale-fslc https://github.com/Freescale/linux-fslc
        git fetch --no-tags freescale-fslc 6.6-2.0.x-imx
        git checkout 49e0afc879aa92d4c9ff99b7b92a6ee5d4ba127b
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/clk/imx/ drivers/firmware/imx/ drivers/mailbox/ drivers/mtd/spi-nor/ drivers/phy/freescale/ drivers/pinctrl/freescale/ drivers/rpmsg/