Revert "wandboard: Remove unnecessary delay"

This reverts commit b8b9790e.

Some wandboard variants no longer boot after this commit, so keep
the original delay to avoid the boot regression.

Reported-by: Varga Zsolt <vazso@vazso.hu>
Tested-by: Varga Zsolt <vazso@vazso.hu>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>