arm64: sve: Provide a conditional update accessor for ZCR_ELx

mainline inclusion
from mainline-v5.13-rc1
commit 71ce1ae5
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8E73O
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=71ce1ae56e4d43a0c568e2d4bfb154cd15306a82



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A common pattern is to conditionally update ZCR_ELx in order
to avoid the "self-synchronizing" effect that writing to this
register has.

Let's provide an accessor that does exactly this.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>