Do not prefer Apple MPS (#8446)

Require explicit request for MPS, i.e.
```bash
python detect.py --device mps
```

Reverts https://github.com/ultralytics/yolov5/pull/8210 for preferring MPS if available.

Note that torch MPS is experiencing ongoing compatibility issues in https://github.com/pytorch/pytorch/issues/77886

utils/torch_utils.py

@@ -62,7 +62,7 @@ def select_device(device='', batch_size=0, newline=True):
         assert torch.cuda.is_available() and torch.cuda.device_count() >= len(device.replace(',', '')), \
             f"Invalid CUDA '--device {device}' requested, use '--device cpu' or pass valid CUDA device(s)"
 
-    if not cpu and torch.cuda.is_available():  # prefer GPU if available
+    if not (cpu or mps) and torch.cuda.is_available():  # prefer GPU if available
         devices = device.split(',') if device else '0'  # range(torch.cuda.device_count())  # i.e. 0,1,6,7
         n = len(devices)  # device count
         if n > 1 and batch_size > 0:  # check batch_size is divisible by device_count
@@ -72,7 +72,7 @@ def select_device(device='', batch_size=0, newline=True):
             p = torch.cuda.get_device_properties(i)
             s += f"{'' if i == 0 else space}CUDA:{d} ({p.name}, {p.total_memory / (1 << 20):.0f}MiB)\n"  # bytes to MB
         arg = 'cuda:0'
-    elif not cpu and getattr(torch, 'has_mps', False) and torch.backends.mps.is_available():  # prefer MPS if available
+    elif mps and getattr(torch, 'has_mps', False) and torch.backends.mps.is_available():  # prefer MPS if available
         s += 'MPS\n'
         arg = 'mps'
     else:  # revert to CPU