Kernel: Rework sleeping API

instead of sleep_{ns,ms} we now have sleep_{for,until}_{ns,ms}. This
makes code cleaner that just wants to sleep until some timestamp

kernel/kernel/FS/DevFS/FileSystem.cpp

@@ -50,6 +50,7 @@ namespace Kernel
 			[](void* _devfs)
 			{
 				auto* devfs = static_cast<DevFileSystem*>(_devfs);
+				uint64_t next_update_ms = SystemTimer::get().ms_since_boot();
 				while (true)
 				{
 					{
@@ -57,7 +58,8 @@ namespace Kernel
 						for (auto& device : devfs->m_devices)
 							device->update();
 					}
-					SystemTimer::get().sleep_ms(10);
+					SystemTimer::get().sleep_until_ms(next_update_ms);
+					next_update_ms += 10;
 				}
 			}, s_instance
 		));

kernel/kernel/FS/VirtualFileSystem.cpp

@@ -157,7 +157,7 @@ namespace Kernel
 			if (i == 4)
 				dwarnln("Could not find specified root device, waiting for it to get loaded...");
 
-			SystemTimer::get().sleep_ms(sleep_ms);
+			SystemTimer::get().sleep_for_ms(sleep_ms);
 		}
 
 		derrorln("Could not find root device '{}' after {} ms", root_path, timeout_ms);