Use symbols for cmos offsets in ram_probe()

Use symbols for cmos offsets in ram_probe()

This patches uses symbols for cmos offsets when calculating ram size
in ram_probe()
Besides, it adds some cmos offset symbols into cmos.h, and changes
some memory cmos offset to be more meaningful.

Signed-off-by: Nguyen Anh Quynh <aquynh@gmail.com>