The man behind the Spurs dynasty isn’t chasing another trophy. He’s chasing more grazing land in the middle of the Pacific. Peter J. Holt, the longtime principal owner of the San Antonio Spurs , has quietly expanded his footprint in Hawaii with an $8 million off-market land purchase that adds another 100 acres to his growing Big Island cattle ranch, The Post has learned.  The transaction increases Holt’s holdings to roughly 900 acres on the slopes above the Waipio Valley corridor — one of the