feature: L0 Device Hierarchy support for Composite & Flat modes

Related-To: LOCI-4615

- Added Support for users to set ZE_FLAT_DEVICE_HIERARCHY to either FLAT
or COMPOSITE to change how devices are returned in zeDeviceGet and
clGetDeviceIDs.
- COMPOSITE is default behavior that exists today.
- FLAT returns all sub devices which have no sub devices and all root
devices that have no sub devices in zeDeviceGet ie with all devices
flattened out in order.
- Added zeDeviceGetRootDevice for one to retrieve the Root Device for
any SubDevice.

Signed-off-by: Neil R Spruit <neil.r.spruit@intel.com>

opencl/source/api/api.cpp

@@ -262,6 +262,10 @@ cl_int CL_API_CALL clGetDeviceIDs(cl_platform_id platform,
                 exposeSubDevices = DebugManager.flags.ReturnSubDevicesAsApiDevices.get();
             }
 
+            if (pPlatform->peekExecutionEnvironment()->isExposingSubDevicesAsDevices()) {
+                exposeSubDevices = true;
+            }
+
             ClDevice *device = pPlatform->getClDevice(platformDeviceIndex);
             UNRECOVERABLE_IF(device == nullptr);