Procedure

1. Get 64Bit Cross Compiler by sudo apt-get install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu

2. Build according to bcmrpi3_defconfig (Raspberry Pi 3B+) make -j4 ARCH=arm64 KERNEL=kernel7 CROSS_COMPILE=aarch64-linux-gnu- bcmrpi3_defconfig

3. Do Modification of Kernel through menuconfig make -j4 ARCH=arm64 KERNEL=kernel7 CROSS_COMPILE=aarch64-linux-gnu- menuconfig

4. Make Kernel make -j4 ARCH=arm64 KERNEL=kernel7 CROSS_COMPILE=aarch64-linux-gnu-

5. Make Module files for this Kernel make -j4 ARCH=arm64 KERNEL=kernel7 CROSS_COMPILE=aarch64-linux-gnu- modules

Reference (In Traditional Chinese Only) https://blog.gtwang.org/iot/raspberry-pi-compile-linux-kernel/