i can customize and build android kernel separately from android system as discribed in Android_User's_Guide.pdf, but when build android system, kernel config replaced to some kind of default config (imx_v7_android_defconfig I think)
I apologize for the delay.
Actually, that is one of the solutions.
This is because at the time you are initializing the Android environment. You are setting the options that are by default in the defconfig file. One of the solutions is making what you did, another one could be the only modifying or adding the configuration to the defconfig file.
Hope this information can help you.
find temprorary hack solution - make menuconfig whith script
cp ./out/target/product/sabresd_6dq/obj/KERNEL_OBJ/.config ./vendor/nxp-opensource/kernel_imx
cp .config ./arch/arm/configs/imx_v7_android_defconfig