ANDROID: KVM: arm64: pkvm: Lazy host FP save/restore

Implement lazy save/restore of the FPSIMD and SVE registers for the host
so that the guest register state remains live for a vCPU with
KVM_ARM64_FP_ENABLED set and the state is only switched in response to a
trap from the host.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Bug: 209580772
Change-Id: I6977740727964e297d1e658e8eaec4f0125cce48
Signed-off-by: Will Deacon <willdeacon@google.com>