powerpc/mpc8xxx: Fix DDR code for empty first DIMM slot and enable DQS_en

Check second DIMM slot in case the first one is empty.
Honor DQS enable option for SDRAM mode register.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
2 files changed