arm64: add machine check safe sysctl interface

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5GB28


CVE: NA

-------------------------------

Add /proc/sys/kernel/machine_check_safe_enable. Set 1(default value) to
enable machine check safe support. Set 0(default) to disable machine
check safe support.

Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>