OMAP3:SDRC: introduce DDR types

OMAP3:SDRC: introduce DDR types

Micron DDR timings based on:
http://www.sakoman.net/cgi-bin/gitweb.cgi?p=x-load-omap3.git;a=blob;f=include/asm/arch-omap3/mem.h;h=e6fbfe3947f5d0d85fea776e30821d4017316d86;hb=HEAD

Introduce Micron DDR timings and provide
CONFIG_OMAP3_INFINEON_DDR and CONFIG_OMAP3_MICRON_DDR config
options to allow for platform files to setup their timings as
per the type of DDR selected

Reported-by: Steve Sakoman in http://www.nabble.com/forum/Permalink.jtp?root=25779518&post=25959734&page=y
Signed-off-by: Nishanth Menon <nm@ti.com>