Refactor device determination to function; add MPS fallback

tools/latent_upscaler.py

@@ -15,6 +15,8 @@ from torch import nn
 from tqdm import tqdm
 from PIL import Image
 
+from library.device_utils import get_preferred_device
+
 
 class ResidualBlock(nn.Module):
     def __init__(self, in_channels, out_channels=None, kernel_size=3, stride=1, padding=1):
@@ -255,7 +257,7 @@ def create_upscaler(**kwargs):
 
 # another interface: upscale images with a model for given images from command line
 def upscale_images(args: argparse.Namespace):
-    DEVICE = torch.device("cuda" if torch.cuda.is_available() else "cpu")
+    DEVICE = get_preferred_device()
     us_dtype = torch.float16  # TODO: support fp32/bf16
     os.makedirs(args.output_dir, exist_ok=True)