Do not permit "custom" or "automatic" in dpctl.SyclPlatform.get_devices

These device types act unexpectedly in DPC++ 2025.0.4, returning the same result as `sycl::info::device_type::all`, so use unknown device and return an empty list instead

Author: ndgrigorian

dpctl/_sycl_platform.pyx

@@ -413,12 +413,8 @@ cdef class SyclPlatform(_SyclPlatform):
                 DTy = _device_type._ACCELERATOR
             elif dty_str == "all":
                 DTy = _device_type._ALL_DEVICES
-            elif dty_str == "automatic":
-                DTy = _device_type._AUTOMATIC
             elif dty_str == "cpu":
                 DTy = _device_type._CPU
-            elif dty_str == "custom":
-                DTy = _device_type._CUSTOM
             elif dty_str == "gpu":
                 DTy = _device_type._GPU
             else:
@@ -428,12 +424,8 @@ cdef class SyclPlatform(_SyclPlatform):
                 DTy = _device_type._ALL_DEVICES
             elif device_type == device_type_t.accelerator:
                 DTy = _device_type._ACCELERATOR
-            elif device_type == device_type_t.automatic:
-                DTy = _device_type._AUTOMATIC
             elif device_type == device_type_t.cpu:
                 DTy = _device_type._CPU
-            elif device_type == device_type_t.custom:
-                DTy = _device_type._CUSTOM
             elif device_type == device_type_t.gpu:
                 DTy = _device_type._GPU
             else: