Add platform_caps.c to maintain platform related information
Set platform_caps.pi to true if all iommus are posted interrupt capable, false
otherwise
If lapic passthru is not configured and platform_caps.pi is true, the vm
may be able to use posted interrupt for a ptdev, if the ptdev's IRQ is
single-destination
Tracked-On: #4506
Signed-off-by: dongshen <dongsheng.x.zhang@intel.com>
Reviewed-by: Eddie Dong <eddie.dong@Intel.com>
