Steps:
1, build-chain prepare
      https://occ-oss-prod.oss-cn-hangzhou.aliyuncs.com/resource/1836682/1640771208032/Xuantie-900-gcc-linux-5.10.4-glibc-x86_64-V2.2.4-20211227.tar.gz
      set PATH env, for example:
	  PATH=$PATH:/path/to/build-chain/bin
2, build kernel
      git clone git@gitee.com:openanolis/riscv-cloud-kernel.git
      cd riscv-cloud-kernel
      git checkout devel-5.10
      make -j16 CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv light_defconfig
      make -j16 CROSS_COMPILE=riscv64-unknown-linux-gnu- ARCH=riscv
3, set KERNELDIR env as the kernel dir
      for example:
          export KERNELDIR=/path/to/anolis/riscv-cloud-kernel/
4, just run "make"
5, get the files in output dir
6, run "make clean" to do the cleanup