Added property parent_device

This returns None for root devices, but returns a SyclDevice for
a sub-device.

Added cpdef method equals, and Python method __eq__

```
Python 3.7.9 (default, Mar 10 2021, 05:18:00)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.22.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import dpctl

In [2]: cpu_device = dpctl.SyclDevice("cpu")

In [3]: cpu_device == cpu_device
Out[3]: True

In [4]: cpu_device2 = dpctl.SyclDevice("cpu")

In [5]: cpu_device == cpu_device2
Out[5]: True

In [6]: [d1, d2, d3 ] =cpu_device.create_sub_devices(partition=4)

In [7]: d1.parent_device == cpu_device
Out[7]: True

In [8]: d2.parent_device == cpu_device
Out[8]: True

In [9]: d3.parent_device == cpu_device
Out[9]: True
```

Author: oleksandr-pavlyk

dpctl/_sycl_device.pxd

@@ -25,10 +25,11 @@ from ._backend cimport (
     DPCTLSyclDeviceSelectorRef,
     _partition_affinity_domain_type
 )
+from libcpp cimport bool as cpp_bool
 
 
 cdef class _SyclDevice:
-    ''' Wrapper class for a Sycl Device
+    ''' Wrapper data owner class for a Sycl Device
     '''
     cdef DPCTLSyclDeviceRef _device_ref
     cdef const char *_vendor_name
@@ -48,3 +49,4 @@ cdef class SyclDevice(_SyclDevice):
     cdef list create_sub_devices_equally(self, size_t count)
     cdef list create_sub_devices_by_counts(self, object counts)
     cdef list create_sub_devices_by_affinity(self, _partition_affinity_domain_type domain)
+    cpdef cpp_bool equals(self, SyclDevice q)

dpctl/_sycl_device.pyx

@@ -34,6 +34,7 @@ from ._backend cimport (
     DPCTLDeviceVector_Delete,
     DPCTLDeviceVector_GetAt,
     DPCTLDeviceVector_Size,
+    DPCTLDevice_AreEq,
     DPCTLDevice_GetBackend,
     DPCTLDevice_GetDeviceType,
     DPCTLDevice_GetDriverInfo,
@@ -74,6 +75,7 @@ from ._backend cimport (
     DPCTLDevice_CreateSubDevicesEqually,
     DPCTLDevice_CreateSubDevicesByCounts,
     DPCTLDevice_CreateSubDevicesByAffinity,
+    DPCTLDevice_GetParentDevice,
 )
 from . import backend_type, device_type
 from libc.stdint cimport uint32_t
@@ -96,7 +98,7 @@ cdef class SubDeviceCreationError(Exception):
 
 
 cdef class _SyclDevice:
-    """ A helper metaclass to abstract a cl::sycl::device instance.
+    """ A helper data-owner class to abstract a cl::sycl::device instance.
     """
 
     def __dealloc__(self):
@@ -714,3 +716,23 @@ cdef class SyclDevice(_SyclDevice):
                 return self.create_sub_devices_equally(partition)
             except Exception as e:
                 raise TypeError("Unsupported type of sub-device argument")
+
+    @property
+    def parent_device(self):
+        cdef DPCTLSyclDeviceRef pDRef = NULL
+        pDRef = DPCTLDevice_GetParentDevice(self._device_ref)
+        if (pDRef is NULL):
+            return None
+        return SyclDevice._create(pDRef)
+
+    cpdef cpp_bool equals(self, SyclDevice other):
+        """ Returns true if the SyclDevice argument has the same _device_ref
+            as this SyclDevice.
+        """
+        return DPCTLDevice_AreEq(self._device_ref, other.get_device_ref())
+
+    def __eq__(self, other):
+        if isinstance(other, SyclDevice):
+            return self.equals(<SyclDevice> other)
+        else:
+            return False