KABI: Add CONFIG_KABI_RESERVE to control KABI padding reserve

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4K3S5



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Add CONFIG_KABI_RESERVE to control KABI padding reserve or not,
for some embedded system, KABI padding reserve may be not necessary.

By the way, adjust unsigned long to u64 to unify basic reserve
length for both 32bit and 64bit architectures.

Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>