kunit: tool: Add support for overriding the QEMU serial port

On some platforms, the console is not the first serial port. To make
this work, the first serial port in QEMU must be set to "null".

Add support for this by adding an optional "serial" parameter, which
defaults to "stdio", and can be overridden by platform-specific
configuration.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: David Gow <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/kunit/kunit_kernel.py

···
 		self._kernel_path = qemu_arch_params.kernel_path
 		self._kernel_command_line = qemu_arch_params.kernel_command_line + ' kunit_shutdown=reboot'
 		self._extra_qemu_params = qemu_arch_params.extra_qemu_params
+		self._serial = qemu_arch_params.serial
 
 	def make_arch_config(self, base_kunitconfig: kunit_config.Kconfig) -> kunit_config.Kconfig:
 		kconfig = kunit_config.parse_from_string(self._kconfig)
···
 				'-append', ' '.join(params + [self._kernel_command_line]),
 				'-no-reboot',
 				'-nographic',
-				'-serial', 'stdio'] + self._extra_qemu_params
+				'-serial', self._serial] + self._extra_qemu_params
 		# Note: shlex.join() does what we want, but requires python 3.8+.
 		print('Running tests with:\n$', ' '.join(shlex.quote(arg) for arg in qemu_command))
 		return subprocess.Popen(qemu_command,

tools/testing/kunit/qemu_config.py

···
   kernel_path: str
   kernel_command_line: str
   extra_qemu_params: List[str]
+  serial: str = 'stdio'