kunit: qemu_configs: SH: Respect kunit cmdline

The default SH kunit configuration sets CONFIG_CMDLINE_OVERWRITE which
completely disregards the cmdline passed from the bootloader/QEMU in favor
of the builtin CONFIG_CMDLINE.
However the kunit tool needs to pass arguments to the in-kernel kunit core,
for filters and other runtime parameters.

Enable CONFIG_CMDLINE_EXTEND instead, so kunit arguments are respected.

Link: https://lore.kernel.org/r/20250407-kunit-sh-v1-1-f5432a54cf2f@linutronix.de
Fixes: 8110a3c ("kunit: tool: Add support for SH under QEMU")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: t-8ch

tools/testing/kunit/qemu_configs/sh.py

@@ -7,7 +7,9 @@
 CONFIG_MEMORY_START=0x0c000000
 CONFIG_SH_RTS7751R2D=y
 CONFIG_RTS7751R2D_PLUS=y
-CONFIG_SERIAL_SH_SCI=y''',
+CONFIG_SERIAL_SH_SCI=y
+CONFIG_CMDLINE_EXTEND=y
+''',
 			   qemu_arch='sh4',
 			   kernel_path='arch/sh/boot/zImage',
 			   kernel_command_line='console=ttySC1',