mpc83xx: Rename CONFIG_SYS_DDR_CONFIG and cleanup DDR csbnds code

mpc83xx: Rename CONFIG_SYS_DDR_CONFIG and cleanup DDR csbnds code

Rename CONFIG_SYS_DDR_CONFIG to include which CS it is configuring
Cleanup the setting of the csnbds to respect the setting of
CONFIG_SYS_DDR_SDRAM_BASE
Use __ilog2 instead of writing the code to compute it
Disable unused CS configs
Ensure ddrlaw.bar is configured

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Cc: Joe Hershberger <joe.hershberger@gmail.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>