arm64/sve: Make access to FFR optional

mainline inclusion
from mainline-v5.16-rc1
commit 9f584866
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=9f5848665788a0f07bc175cb2cdd06d367b7556e



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SME introduces streaming SVE mode in which FFR is not present and the
instructions for accessing it UNDEF. In preparation for handling this
update the low level SVE state access functions to take a flag specifying
if FFR should be handled. When saving the register state we store a zero
for FFR to guard against uninitialized data being read. No behaviour change
should be introduced by this patch.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211019172247.3045838-5-broonie@kernel.org


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