kconfig: Add script to check & update openeuler_defconfig

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7LEY4
bugzilla: https://gitee.com/openeuler/kernel/issues/I68D0O
bugzilla: https://gitee.com/openeuler/kernel/issues/I63KVP

Reference: https://gitee.com/openeuler/kernel/pulls/286
Reference: https://gitee.com/openeuler/kernel/commit/ca1af5899ef7c1e1617913ecee37d53972f701fb

If new options are introduced, but openeuler_defconfig is not explicitly
configured, the actual compiled version may be configured according to
the default settings, which may be different from the author's expectation.
Therefore, the some command is added to help developers to check and update
the defconfig. It is also convenient for continuous integration tools to
check the consistency of defconfig.

```
Usage:
  make check_oedefconfig
  #
  # New options might needs to be updated to the default configuration
  # file. Use the following command:
  # 'make openeuler_defconfig/menuconfig/update_oedefconfig/save_oedefconfig'
  # !!! DO NOT EDIT !!!
  #
  # defconfig: arch/arm64/configs/openeuler_defconfig
  #
  CONFIG_MEMCG=n
  CONFIG_BLK_CGROUP=n
  CONFIG_CFS_BANDWIDTH=n
  CONFIG_RT_GROUP_SCHED=n
  CONFIG_CGROUP_PIDS=n
  CONFIG_CGROUP_RDMA=n
  CONFIG_CGROUP_FREEZER=n
  CONFIG_CGROUP_HUGETLB=n
  CONFIG_CPUSETS=n

  make update_oedefconfig
  # Update openeuler_defconfig base on current source code

  make save_oedefconfig
  # Save current .config to openeuler_defconfig'
```

If someone adds a new Kconfig, he should also explicitly update
openeuler_defconfig, whether it's enabled or disabled.

Again, do *NOT* edit openeuler_defconfig directly.

Link: https://gitee.com/openeuler/kernel/pulls/286


Signed-off-by: Liu Chao <liuchao173@huawei.com>
Cc: Jason Zeng <jason.zeng@intel.com>
Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com>