cleanup: SMBUS_MEM_DEVICE_[START|END]

[Stefan Reinauer]

Hi,

the two config variables SMBUS_MEM_DEVICE_START and SMBUS_MEM_DEVICE_END
are only used by ./src/sdram/generic_dump_spd.c.

Does it make sense to keep those?  dump_spd_registers() could
use the ram_controller struct to get the values. Then I would remove 
SMBUS_MEM_DEVICE_[START|END] occurences in the code.

Stefan