feat: add fadt based lapic timer calibration

kernel/include/acpi/discovery.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include "acpi/acpi.h"
+#include "acpi/fadt.h"
+#include "acpi/madt.h"
+#include "util/optional.h"
+
+namespace acpi {
+
+struct discovery_result_t {
+    optional<Rsdp> rsdp;
+    optional<Madt> madt;
+    // TODO(wiring): capture the FADT in setupAcpi and store it here
+    optional<Fadt> fadt;
+};
+
+} // namespace acpi