powerpc/mpc8xxx: Enable calculation for fixed DDR chips

We used to have fixed parameters for soldered DDR chips. This patch
introduces CONFIG_SYS_DDR_RAW_TIMING to enable calculation based on timing
data from DDR chip datasheet, implemneted in board-specific files or header
files.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/README b/README
index 2da0f96..1e2d4d3 100644
--- a/README
+++ b/README
@@ -2948,6 +2948,12 @@
 		one, specify here. Note that the value must resolve
 		to something your driver can deal with.
 
+- CONFIG_SYS_DDR_RAW_TIMING
+		Get DDR timing information from other than SPD. Common with
+		soldered DDR chips onboard without SPD. DDR raw timing
+		parameters are extracted from datasheet and hard-coded into
+		header files or board specific files.
+
 - CONFIG_SYS_83XX_DDR_USES_CS0
 		Only for 83xx systems. If specified, then DDR should
 		be configured using CS0 and CS1 instead of CS2 and CS3.