Kernel: Rewrite whole AML parser

Now AML parsing is actually done while respecting namespaces and
scopes. I implemented the minimal functionality to parse qemu's AML.

Next step is to implement AML interpreting and then we can drop lai
as a dependency.

kernel/include/kernel/ACPI/AML/Pkg.h

@@ -0,0 +1,51 @@
+#pragma once
+
+#include <BAN/ByteSpan.h>
+#include <BAN/Optional.h>
+
+namespace Kernel::ACPI::AML
+{
+
+	static BAN::Optional<uint32_t> parse_pkg_length(BAN::ConstByteSpan aml_data)
+	{
+		if (aml_data.size() < 1)
+			return {};
+
+		uint8_t lead_byte = aml_data[0];
+		if ((lead_byte & 0xC0) && (lead_byte & 0x30))
+			return {};
+
+		uint32_t pkg_length = lead_byte & 0x3F;
+		uint8_t byte_count = (lead_byte >> 6) + 1;
+
+		if (aml_data.size() < byte_count)
+			return {};
+
+		for (uint8_t i = 1; i < byte_count; i++)
+			pkg_length |= aml_data[i] << (i * 8 - 4);
+
+		return pkg_length;
+	}
+
+	static void trim_pkg_length(BAN::ConstByteSpan& aml_data)
+	{
+		ASSERT(aml_data.size() >= 1);
+		uint8_t byte_count = (aml_data[0] >> 6) + 1;
+		aml_data = aml_data.slice(byte_count);
+	}
+
+	static BAN::Optional<BAN::ConstByteSpan> parse_pkg(BAN::ConstByteSpan& aml_data)
+	{
+		auto pkg_length = parse_pkg_length(aml_data);
+		if (!pkg_length.has_value())
+			return {};
+
+		auto result = aml_data.slice(0, pkg_length.value());
+		trim_pkg_length(result);
+
+		aml_data = aml_data.slice(pkg_length.value());
+
+		return result;
+	}
+
+}