[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/process.h

@@ -24,6 +24,8 @@ public:
 	/// Destructor.
 	virtual ~process();
 
+	static constexpr kobject::type type = kobject::type::process;
+
 	/// Get the currently executing process.
 	static process & current();