board: ls1046ardb: fix defconfig overlay

This patch is to fix issue #71473.

The commit 0be0d217 revert some change
introduced by hwmv2 which allows defconfig can be overlay, so revert
back defconfig to be full configure files which includes all items used
by the board variants.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>