target/i386/kvm: Report which action failed in kvm_arch_put/get_registers

target/i386/kvm: Report which action failed in kvm_arch_put/get_registers

To help debug and triage future failure reports (akin to [1,2]) that
may occur during kvm_arch_put/get_registers, the error path of each
action is accompanied by unique error message.

[1] https://issues.redhat.com/browse/RHEL-7558
[2] https://issues.redhat.com/browse/RHEL-21761

Signed-off-by: Julia Suvorova <jusual@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240927104743.218468-3-jusual@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>