vdso: do cntvct workaround in the VDSO

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8LFBU


CVE: NA

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If a cntvct workaround is enabled, read CNTVCT_EL0 twice
in VDSO to avoid the clock bug.

Without this patch on Kunpeng916:
./gettimeofday -E -C 200 -L -S -W -N "gettimeofday"
Running:        gettimeofday# ./gettimeofday -E -C 200 -L -S -W -N gettimeofday
             prc thr   usecs/call      samples   errors cnt/samp
gettimeofday   1   1      0.31753          198        0    20000

With this patch on Kunpeng916:
./gettimeofday -E -C 200 -L -S -W -N "gettimeofday"
Running:        gettimeofday# ./gettimeofday -E -C 200 -L -S -W -N gettimeofday
             prc thr   usecs/call      samples   errors cnt/samp
gettimeofday   1   1      0.05244          198        0    20000

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>