Add a yellowstone stub and partially migrate denali

sys/yellowstone/stub/yellowstone_stub.cpp

@@ -1,3 +1,23 @@
-// PLACEHOLDER
-#include <stdint.h>
-uint64_t a = 0;
+#include "include/yellowstone_stub.h"
+
+#include "include/yellowstone.h"
+
+namespace {
+
+const uint64_t kPciSize = 0x1000;
+
+}  // namespace
+
+YellowstoneStub::YellowstoneStub(z_cap_t yellowstone_cap)
+    : yellowstone_stub_(EndpointClient::AdoptEndpoint(yellowstone_cap)) {}
+
+glcr::ErrorOr<MappedMemoryRegion> YellowstoneStub::GetAhciConfig() {
+  YellowstoneGetReq req{
+      .type = kYellowstoneGetAhci,
+  };
+  ASSIGN_OR_RETURN(
+      YellowstoneGetAhciResp resp,
+      (yellowstone_stub_
+           ->CallEndpoint<YellowstoneGetReq, YellowstoneGetAhciResp>(req)));
+  return MappedMemoryRegion::DirectPhysical(resp.ahci_phys_offset, kPciSize);
+}