Kernel: Implement unified input files for device hot-plugging support

/dev/keyboard and /dev/mouse can be read for events from any attached
keyboard or mouse respectively. This makes device hot-plugging support
pretty much automatic for TTY, GUI, and whatever takes input.

userspace/tests/test-mouse/main.cpp

@@ -50,7 +50,7 @@ void cleanup()
 int main(int argc, char** argv)
 {
 	const char* fb_path = "/dev/fb0";
-	const char* mouse_path = "/dev/mouse0";
+	const char* mouse_path = "/dev/mouse";
 
 	if (argc == 1)
 		;