KVM: arm/arm64: Add a vcpu feature for pointer authentication

This patch adds a runtime capabality for KVM tool to enable Arm64 8.3
Pointer Authentication in guest kernel. Two vcpu features
KVM_ARM_VCPU_PTRAUTH_[ADDRESS/GENERIC] are supplied together to enable
Pointer Authentication in KVM guest after checking the capability.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com> [merge new kernel heaers]
Signed-off-by: Will Deacon <will@kernel.org>