feat(kernel): add RequestPages and ReleasePages syscalls

crates/kernel/src/lib.rs

@@ -125,6 +125,10 @@ impl<P: Platform> Kernel<P> {
         }
     }
 
+    pub fn free_page_count(&self) -> usize {
+        self.page_pool.free_count()
+    }
+
     pub fn process_exists(&self, pid: ProcessId) -> bool {
         self.processes.get(pid).is_ok()
     }