x86/KVM: Convert to fpstate

x86/KVM: Convert to fpstate

BugLink: https://bugs.launchpad.net/bugs/1967750
Convert KVM code to the new register storage mechanism in preparation for
dynamically sized buffers.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Link: https://lkml.kernel.org/r/20211013145322.451439983@linutronix.de
(cherry picked from commit 1c57572d754fc54e0b8ac0df5350969ce6292d12)
Acked-by: Dimitri John Ledkov <dimitri.ledkov@canonical.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>