hw/xen: Extract 'xen_igd.h' from 'xen_pt.h'

"hw/xen/xen_pt.h" requires "hw/xen/xen_native.h" which is target
specific. It also declares IGD methods, which are not target
specific.

Target-agnostic code can use IGD methods. To allow that, extract
these methos into a new "hw/xen/xen_igd.h" header.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20231114143816.71079-18-philmd@linaro.org>
8 files changed