arm64: openeuler_defconfig: increase CONFIG_NR_CPUS value to 4096

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4J96Y


CVE: NA

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Set CONFIG_NR_CPUS of openeuler_defconfig to 4096 to meet
scalability requirement for arm64.

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