KVM: x86: pass the whole hflags field to emulator and back

The hflags field will contain information about system management mode
and will be useful for the emulator.  Pass the entire field rather than
just the guest-mode information.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>