KVM: arm64: Move guest_owns_fp_regs() to increase its scope

KVM: arm64: Move guest_owns_fp_regs() to increase its scope

guest_owns_fp_regs() will be used to check fpsimd state ownership
across kvm/arm64. Therefore, move it to kvm_host.h to widen its
scope.

Moreover, the host state is not per-vcpu anymore, the vcpu
parameter isn't used, so remove it as well.

No functional change intended.

Signed-off-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240423150538.2103045-3-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>