[kernel] Add syscall helpers

Added the syscalls/helpers.h file to templatize common kobject syscall
operations. Also moved most syscall implementations to using
process::current() and thread::current() instead of asking the
scheduler.

src/kernel/objects/event.h

@@ -10,4 +10,6 @@ class event :
 public:
 	event() :
 		kobject(type::event) {}
+
+	static constexpr kobject::type type = kobject::type::event;
 };