mpc85xx: Base emulator support

Prepare for emulator support for mpc85xx parts.
Disable DDR training and skip wrlvl_cntl_2 and wrlvl_cntl_3 registers.
These two registers improve stability but not supported by emulator.
Add CONFIG_FSL_TBCLK_EXTRA_DIV for possible adjustment to time base.

Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/README b/README
index a5c3e8d..5fb4c75 100644
--- a/README
+++ b/README
@@ -413,6 +413,10 @@
 		CONFIG_SYS_FSL_DSP_CCSRBAR_DEFAULT
 		This value denotes start offset of DSP CCSR space.
 
+		CONFIG_SYS_FSL_DDR_EMU
+		Specify emulator support for DDR. Some DDR features such as
+		deskew training are not available.
+
 - Generic CPU options:
 		CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIAN