[kernel] Consolodate koid and close syscalls

A number of object types had _close or _koid syscalls. Moved those to be
generic for kobject.

src/kernel/syscalls/helpers.h

@@ -3,6 +3,7 @@
 /// Utility functions for use in syscall handler implementations
 
 #include "j6/types.h"
+#include "objects/kobject.h"
 #include "objects/process.h"
 
 namespace syscalls {
@@ -26,6 +27,13 @@ T * get_handle(j6_handle_t handle)
 	return static_cast<T*>(o);
 }
 
+template <>
+inline kobject * get_handle<kobject>(j6_handle_t handle)
+{
+	process &p = process::current();
+	return p.lookup_handle(handle);
+}
+
 template <typename T>
 T * remove_handle(j6_handle_t handle)
 {