Explainer-What is CXMT and how did it become China's DRAM champion? By Eduardo Baptista BEIJING, July 15 (Reuters) - China's ChangXin Memory Technologies (CXMT) expects to raise at least 57.9 billion yuan ($8.6 billion) this month in an initial public offering on Shanghai's Nasdaq-style STAR Market in what would be Asia's largest share sale so far this year. The offering, which could rise to 66.6 billion yuan if the over-allotment option is exercised, would mark a major milestone for a company that has grown to become China's leading maker of DRAM memory chips and a symbol of Beijing's push toward technological self-reliance. WHAT IS CXMT? CXMT is China's top maker of dynamic random-access memory (DRAM) chips, which provide short-term memory for smartphones, personal computers, server