Kernel: Add support for power button shutdown

This patch implements basic support for power button using ACPI
fixed events. I still need to implement general purpose events
and embedded controller for full power button support.

kernel/include/kernel/ACPI/ACPI.h

@@ -8,7 +8,7 @@
 namespace Kernel::ACPI
 {
 
-	class ACPI
+	class ACPI : public Interruptable
 	{
 	public:
 		static BAN::ErrorOr<void> initialize();
@@ -31,10 +31,16 @@ namespace Kernel::ACPI
 		// This function will return only if there was an error
 		void poweroff();
 
+		void handle_irq() override;
+
 	private:
 		ACPI() = default;
 		BAN::ErrorOr<void> initialize_impl();
 
+		FADT& fadt() { return *m_fadt; }
+
+		void acpi_event_task();
+
 	private:
 		paddr_t m_header_table_paddr = 0;
 		vaddr_t m_header_table_vaddr = 0;
@@ -49,6 +55,10 @@ namespace Kernel::ACPI
 		};
 		BAN::Vector<MappedPage> m_mapped_headers;
 
+		FADT* m_fadt { nullptr };
+
+		Semaphore m_acpi_event_semaphore;
+
 		bool m_hardware_reduced { false };
 		BAN::RefPtr<AML::Namespace> m_namespace;
 	};

kernel/include/kernel/Process.h

@@ -144,6 +144,7 @@ namespace Kernel
 
 		BAN::ErrorOr<long> sys_sync(bool should_block);
 
+		static BAN::ErrorOr<long> clean_poweroff(int command);
 		BAN::ErrorOr<long> sys_poweroff(int command);
 
 		BAN::ErrorOr<void> mount(BAN::StringView source, BAN::StringView target);