boards: x86/acrn: add devicetree PCIe controller node

Commit 940c66f8 added a bunch of
ACPI PNP ID to x86 boards but skipped those for ACRN. And commit
34a2fbfb changed the behavior of
PCIe controller to looking for PNP ID, it results in compilation
error due to build asserts. So add the PCIe controller node to
the ACRN base DTS file.

Fixes #68956

Signed-off-by: Daniel Leung <daniel.leung@intel.com>