kunit: Extend kconfig help text for KUNIT_UML_PCI

kunit: Extend kconfig help text for KUNIT_UML_PCI

Checkpatch.pl expects at least 4 lines of help text.

Extend the help text to make checkpatch.pl happy.

Link: https://lore.kernel.org/r/20250916-kunit-pci-kconfig-v1-1-6d1369f06f2a@linutronix.de
Fixes: 031cdd3bc3f3 ("kunit: Enable PCI on UML without triggering WARN()")
Suggested-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/lkml/3dc95227-2be9-48a0-bdea-3f283d9b2a38@linuxfoundation.org/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>