s390: rename default_defconfig to debug_defconfig

The name debug_defconfig reflects what the config is actually good
for and should be less confusing.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/configs/default_defconfig b/arch/s390/configs/debug_defconfig
similarity index 100%
rename from arch/s390/configs/default_defconfig
rename to arch/s390/configs/debug_defconfig