Top US lawmakers want the Trump administration to launch a formal national security probe into Chinese memory chipmaker CXMT on suspicions that Beijing orchestrated the company’s blockbuster IPO to prop up a key military asset, The Post has learned. Shares for the China-based chipmaker, also known as ChangXin Memory Technologies, skyrocketed 466% in Shanghai trading on Monday — raising $8.6 billion and instantly making the firm the most valuable on a China mainland exchange with a market capitalization of nearly $500 billion. Beijing’s historic windfall — which sent shares of US chipmakers tumbling on competition fears on Monday — is...