gpu-compute, dev-hsa: Remove HSADriver, HSADevice

HSADriver/HSADevice were primarily used with GPUCommandProcessor/
GPUComputeDriver. This change merges the classes together to
simplify the inheritance hierarchy, as well as removing any casting.

Change-Id: I670eb9b49a16c8aba17e13fd1d1287d0621c9f48
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42219
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>

src/dev/hsa/SConscript

@@ -37,12 +37,8 @@ if not env['BUILD_GPU']:
     Return()
 
 SimObject('HSADevice.py')
-SimObject('HSADriver.py')
 
-Source('hsa_device.cc')
-Source('hsa_driver.cc')
 Source('hsa_packet_processor.cc')
 Source('hw_scheduler.cc')
 
-DebugFlag('HSADriver')
 DebugFlag('HSAPacketProcessor')