Add API for saving driver prefs. Save fullscreen state in D3D11 driver.

PortabilityLayer/HostInputDriver.cpp

@@ -0,0 +1,23 @@
+#include "HostInputDriver.h"
+
+namespace PortabilityLayer
+{
+	size_t HostInputDriver::NumInstances()
+	{
+		return ms_numInstances;
+	}
+
+	IGpInputDriver *HostInputDriver::GetInstance(size_t index)
+	{
+		return ms_instances[index];
+	}
+
+	void HostInputDriver::SetInstances(IGpInputDriver *const* instances, size_t numInstances)
+	{
+		ms_instances = instances;
+		ms_numInstances = numInstances;
+	}
+
+	IGpInputDriver *const* HostInputDriver::ms_instances;
+	size_t HostInputDriver::ms_numInstances;
+}