powerpc: Fix CamelCase warnings in DDR related code

Some DDR related structures present in fsl_ddr_dimm_params.h, fsl_ddr_sdram.h, ddr_spd.h
has various parameters with embedded acronyms capitalized that trigger the CamelCase
warning in checkpatch.pl

Convert those variable names to smallcase naming convention and modify all files
which are using these structures with modified structures.

Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>