CRJ-900 Captain reported encountering wake turbulence on arrival into CLT from a B747 inbound to GSP.

Narrative

When in our initial descent with Atlanta Center; we were given the clearance to maintain 290 knots and we were cleared to offset if needed to avoid wake turbulence for what they called a B767. In actuality; it was a larger B747 inbound into GSP. At approximately 12;500 feet MSL; we began to encounter wake turbulence. We began asking for an offset to the left knowing that the departure corridor was just off of our left wing by a few miles. With the wake turbulence becoming worse and the possibility of an upset; we turned approximately 15 degrees left off course and I used a radio transmission to get the attention of the CLT Approach Controller. She had another aircraft 'turn left immediately' to increase separation. We were then told to report level at 10;000 feet MSL; which we complied with. We were about 1.5 to 2 NM offset to the left for quite a few miles till told to proceed direct to RAYCE (the IAF) for the visual to Runway 22 by Greer Approach. Once headed for the approach fix; the rest of the flight continued normally.