KVM: arm64: Rework SVE host-save/guest-restore

mainline inclusion
from mainline-v5.13-rc1
commit 52029198
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=52029198c1cec1e21513d74f87363a0408f28650



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In order to keep the code readable, move the host-save/guest-restore
sequences in their own functions, with the following changes:
- the hypervisor ZCR is now set from C code
- ZCR_EL2 is always used as the EL2 accessor

This results in some minor assembler macro rework.
No functional change intended.

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