Fixing WHPX casing to match SDK

Fixes an issue where the SDK that was releases had a different casing for the
*.h and *.lib files causing a build break if linked directly from Windows Kits.

Signed-off-by: Justin Terry (VM) <juterry@microsoft.com>
Message-Id: <1519665216-1078-2-git-send-email-juterry@microsoft.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Justin Terry (VM) via Qemu-devel <qemu-devel@nongnu.org>