x86/hvm: introduce a flags field in the CPU save record

x86/hvm: introduce a flags field in the CPU save record

Introduce a new flags field and use bit 0 to signal if the FPU has been
initialised or not. Previously Xen always wrongly assumed the FPU was
initialised on restore.

While modifying the FPU restore part of hvm_load_cpu_ctxt remove the
memcpy branching, since v->arch.fpu_ctxt will always point to the right
area for hosts with XSAVE or without it.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>