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>