kunit: qemu_configs: powerpc: Explicitly enable CONFIG_CPU_BIG_ENDIAN=y

The configuration generated by kunit ends up with big endian.
A new kunit configuration for little endian is to be added.
To make the difference clearer spell out the endianness in the kunit
reference config.

Link: https://lore.kernel.org/r/20250415-kunit-ppc-v1-1-f5a170264147@linutronix.de
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/powerpc.py

@@ -3,6 +3,7 @@
 QEMU_ARCH = QemuArchParams(linux_arch='powerpc',
 			   kconfig='''
 CONFIG_PPC64=y
+CONFIG_CPU_BIG_ENDIAN=y
 CONFIG_SERIAL_8250=y
 CONFIG_SERIAL_8250_CONSOLE=y
 CONFIG_HVC_CONSOLE=y''',