Kernel: Implement more AML method invocation stuff

Method invocation is starting to come together. This implemenetation
can interpret some of the qemu's functions to enter ACPI mode.

PCI config space access is currently the one thing is between
entering ACPI mode.

kernel/include/kernel/ACPI/AML/Register.h

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <kernel/ACPI/AML/Node.h>
+
+namespace Kernel::ACPI::AML
+{
+
+	struct Register : public AML::Node
+	{
+		BAN::RefPtr<AML::Node> value;
+
+		Register()
+			: Node(Node::Type::Register)
+		{}
+		Register(BAN::RefPtr<AML::Node> value)
+			: Node(Node::Type::Register)
+			, value(value)
+		{}
+
+		BAN::RefPtr<AML::Node> evaluate() override
+		{
+			if (value)
+				return value->evaluate();
+			return {};
+		}
+
+		bool store(BAN::RefPtr<AML::Node> source) override
+		{
+			auto evaluated = source->evaluate();
+			if (!evaluated)
+			{
+				AML_ERROR("Failed to evaluate source for store");
+				return false;
+			}
+			value = evaluated;
+			return true;
+		}
+
+		void debug_print(int indent) const override
+		{
+			AML_DEBUG_PRINT_INDENT(indent);
+			AML_DEBUG_PRINT("Register\n");
+			if (value)
+				value->debug_print(indent + 1);
+			else
+			{
+				AML_DEBUG_PRINT_INDENT(indent + 1);
+				AML_DEBUG_PRINT("No value\n");
+			}
+		}
+	};
+
+}