When allocating memory for a non-discoverable PCI device's IO, the
current core code removes the XP attribute, allowing code to execute
from that region. This is a security vulnerability and unneeded. This
change updates to mark the region as XP when allocating memory for the
non-discoverable PCI device.
These allocations in this function are limited to `EfiBootServicesData`
and `EfiRuntimeServicesData`, which we expect to be XP.
Signed-off-by: Aaron Pop <aaronpop@microsoft.com>