powerpc/mpc8xxx: Add auto select bank interleaving mode

Based on populated DIMMs, automatically select from cs0_cs1_cs2_cs3 or
cs0_cs1 interleaving, or non-interleaving if not available.

Fix the message of interleaving disabled if controller interleaving
is enabled but DIMMs don't support it.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
diff --git a/doc/README.fsl-ddr b/doc/README.fsl-ddr
index f94b56f..3992640 100644
--- a/doc/README.fsl-ddr
+++ b/doc/README.fsl-ddr
@@ -103,6 +103,11 @@
   # bank(chip-select) interleaving (cs0+cs1+cs2+cs3) (4x1)
   setenv hwconfig "fsl_ddr:bank_intlv=cs0_cs1_cs2_cs3"
 
+  # bank(chip-select) interleaving (auto)
+  setenv hwconfig "fsl_ddr:bank_intlv=auto"
+  This auto mode only select from cs0_cs1_cs2_cs3, cs0_cs1, null dependings
+  on DIMMs.
+
 Memory controller address hashing
 ==================================
 If the DDR controller supports address hashing, it can be enabled by hwconfig.