kconfig: avoid naming conflict OpenBMC Nuvoton layer already uses defconfig for npcm7xx, we need to switch to another name to avoid conflict. Google-Bug-Id: 485233558 Tested: openbmc nuvoton defconfig is applied on nuvoton kernel Change-Id: I96d92a085e9fc91aeab87b4eab19213bbced9726 Signed-off-by: Yuxiao Zhang <yuxiaozhang@google.com>