LibDeviceTree: Add a simple DeviceTree class

This makes it easier to work with device tree nodes and properties, then
writing simple state machines to parse the device tree.
This also makes the old slow traversal methods use the
DeviceTreeProperty helper class, and adds a simple test.

Userland/Libraries/LibDeviceTree/DeviceTree.cpp

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2024, Leon Albrecht <leon.a@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "DeviceTree.h"
+#include "FlattenedDeviceTree.h"
+#include <AK/NonnullOwnPtr.h>
+#include <AK/Types.h>
+
+namespace DeviceTree {
+
+ErrorOr<NonnullOwnPtr<DeviceTree>> DeviceTree::parse(ReadonlyBytes flattened_device_tree)
+{
+    // Device tree must be 8-byte aligned
+    if ((bit_cast<FlatPtr>(flattened_device_tree.data()) & 0b111) != 0)
+        return Error::from_errno(EINVAL);
+
+    auto device_tree = TRY(adopt_nonnull_own_or_enomem(new (nothrow) DeviceTree { flattened_device_tree }));
+    DeviceTreeNodeView* current_node = device_tree.ptr();
+
+    auto const& header = *reinterpret_cast<FlattenedDeviceTreeHeader const*>(flattened_device_tree.data());
+
+    TRY(walk_device_tree(header, flattened_device_tree,
+        {
+            .on_node_begin = [&current_node, &device_tree](StringView name) -> ErrorOr<IterationDecision> {
+                // Skip the root node, which has an empty name
+                if (current_node == device_tree.ptr() && name.is_empty())
+                    return IterationDecision::Continue;
+
+                // FIXME: Use something like children.emplace
+                TRY(current_node->children().try_set(name, DeviceTreeNodeView { current_node }));
+                auto& new_node = current_node->children().get(name).value();
+                current_node = &new_node;
+                return IterationDecision::Continue;
+            },
+            .on_node_end = [&current_node](StringView) -> ErrorOr<IterationDecision> {
+                current_node = current_node->parent();
+                return IterationDecision::Continue;
+            },
+            .on_property = [&device_tree, &current_node](StringView name, ReadonlyBytes value) -> ErrorOr<IterationDecision> {
+                DeviceTreeProperty property { value };
+
+                if (name == "phandle"sv) {
+                    auto phandle = property.as<u32>();
+                    TRY(device_tree->set_phandle(phandle, current_node));
+                }
+
+                TRY(current_node->properties().try_set(name, DeviceTreeProperty { value }));
+                return IterationDecision::Continue;
+            },
+            .on_noop = []() -> ErrorOr<IterationDecision> {
+                return IterationDecision::Continue;
+            },
+            .on_end = [&]() -> ErrorOr<void> {
+                return {};
+            },
+        }));
+
+    return device_tree;
+}
+
+}