add QFN-64 footprint with 4.7x4.7mm exposed pad
Created by: HubertD
as used in Microchip SAMC2x: http://ww1.microchip.com/downloads/en/DeviceDoc/DS60001479B.pdf
Created by: HubertD
as used in Microchip SAMC2x: http://ww1.microchip.com/downloads/en/DeviceDoc/DS60001479B.pdf