Documented pi_device_type

Signed-off-by: Stuart Adams <stuart.adams@codeplay.com>

Author: nyalloc

sycl/include/CL/sycl/detail/pi.h

@@ -132,11 +132,16 @@ typedef enum {
 // make the translation to OpenCL transparent.
 //
 typedef enum : pi_uint64 {
-  PI_DEVICE_TYPE_DEFAULT = CL_DEVICE_TYPE_DEFAULT,
-  PI_DEVICE_TYPE_ALL = CL_DEVICE_TYPE_ALL,
-  PI_DEVICE_TYPE_CPU = CL_DEVICE_TYPE_CPU,
-  PI_DEVICE_TYPE_GPU = CL_DEVICE_TYPE_GPU,
-  PI_DEVICE_TYPE_ACC = CL_DEVICE_TYPE_ACCELERATOR
+  PI_DEVICE_TYPE_DEFAULT =
+      CL_DEVICE_TYPE_DEFAULT, ///< The default device available in the PI
+                              ///< plugin.
+  PI_DEVICE_TYPE_ALL =
+      CL_DEVICE_TYPE_ALL, ///< All devices available in the PI plugin.
+  PI_DEVICE_TYPE_CPU =
+      CL_DEVICE_TYPE_CPU, ///< A PI device that is the host processor.
+  PI_DEVICE_TYPE_GPU = CL_DEVICE_TYPE_GPU, ///< A PI device that is a GPU.
+  PI_DEVICE_TYPE_ACC = CL_DEVICE_TYPE_ACCELERATOR ///< A PI device that is a
+                                                  ///< dedicated accelerator.
 } _pi_device_type;
 
 typedef enum {