Revert "BoardConfigCommon: Set defconfig to JBX-Kernel"

This reverts commit 7feab2f5a28b69002c7ea0b32f6a8faf7aa09ecf.
Revert "Fix external SD-Card mount point"

This reverts commit e78a62db5e686b8d6a96a71c0daae1c79076a841.