WHPX: support for the kernel-irqchip on/off

This patch adds support the kernel-irqchip option for
WHPX with on or off value. 'split' value is not supported
for the option. The option only works for the latest version
of Windows (ones that are coming out on Insiders). The
change maintains backward compatibility on older version of
Windows where this option is not supported.

Signed-off-by: Sunil Muthuswamy <sunilmut@microsoft.com>
Message-Id: <SN4PR2101MB0880B13258DA9251F8459F4DC0170@SN4PR2101MB0880.namprd21.prod.outlook.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>