Tyga -- I'm No Malibu Squatter ... I Got My OWN Mansion

Tyga INSISTS ... he's not some broke-ass squatter who's refusing to pay rent on a Malibu crib -- in fact, he claims he just bought a $6.5-million mansion 20 miles away. TMZ broke the story ... a Malibu landlord named Gholamreza Rezai sued Tyga,…