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/IfElse.h

@@ -0,0 +1,72 @@
+#pragma once
+
+#include <BAN/HashMap.h>
+#include <kernel/ACPI/AML/Node.h>
+#include <kernel/ACPI/AML/ParseContext.h>
+#include <kernel/ACPI/AML/Pkg.h>
+
+namespace Kernel::ACPI::AML
+{
+
+	struct IfElse
+	{
+		static ParseResult parse(ParseContext& context)
+		{
+			ASSERT(context.aml_data.size() >= 1);
+			ASSERT(static_cast<Byte>(context.aml_data[0]) == Byte::IfOp);
+			context.aml_data = context.aml_data.slice(1);
+
+			auto if_pkg = AML::parse_pkg(context.aml_data);
+			if (!if_pkg.has_value())
+				return ParseResult::Failure;
+
+			auto outer_aml_data = context.aml_data;
+			context.aml_data = if_pkg.value();
+
+			auto predicate = AML::parse_object(context);
+			if (!predicate.success())
+				return ParseResult::Failure;
+			auto predicate_node = predicate.node();
+			if (!predicate_node)
+			{
+				AML_ERROR("If predicate is not an integer");
+				return ParseResult::Failure;
+			}
+			auto predicate_integer = predicate_node->as_integer();
+			if (!predicate_integer.has_value())
+			{
+				AML_ERROR("If predicate is not an integer");
+				return ParseResult::Failure;
+			}
+
+			// Else
+			if (!predicate_integer.value())
+			{
+				if (outer_aml_data.size() < 1 || static_cast<Byte>(outer_aml_data[0]) != Byte::ElseOp)
+					context.aml_data = BAN::ConstByteSpan();
+				else
+				{
+					outer_aml_data = outer_aml_data.slice(1);
+					auto else_pkg = AML::parse_pkg(outer_aml_data);
+					if (!else_pkg.has_value())
+						return ParseResult::Failure;
+					context.aml_data = else_pkg.value();
+				}
+			}
+
+			while (context.aml_data.size() > 0)
+			{
+				auto object_result = AML::parse_object(context);
+				if (object_result.returned())
+					return ParseResult(ParseResult::Result::Returned, object_result.node());
+				if (!object_result.success())
+					return ParseResult::Failure;
+			}
+
+			context.aml_data = outer_aml_data;
+
+			return ParseResult::Success;
+		}
+	};
+
+}