Kernel: Replace is_* with kind field

Replaced the is_* virtual functions with a kind field instead

kernel/kernel/Device/Device.cpp

@@ -11,6 +11,7 @@ namespace Kernel
 			MUST(DevFileSystem::get().allocate_inode(create_inode_info(mode, uid, gid))),
 			create_inode_info(mode, uid, gid)
 		)
-	{ }
-
+	{
+		m_kind |= InodeKind::DEVICE;
+	}
 }

kernel/kernel/FS/Pipe.cpp

@@ -39,6 +39,7 @@ namespace Kernel
 		m_blocks = 0;
 		m_dev = 0; // FIXME
 		m_rdev = 0; // FIXME
+		m_kind = InodeKind::PIPE;
 	}
 
 	void Pipe::on_clone(int status_flags)

kernel/kernel/Terminal/TTY.cpp

@@ -74,6 +74,7 @@ namespace Kernel
 		: CharacterDevice(mode, uid, gid)
 		, m_termios(termios)
 	{
+		m_kind |= InodeKind::TTY;
 		m_rdev = next_tty_rdev();
 		m_output.buffer = MUST(ByteRingBuffer::create(PAGE_SIZE));
 	}