Add TQFN-24-1EP_4x4mm_P0.5mm_EP2.1x2.1mm_PullBack

This adds a TQFN24 package with a 4x4mm package and a 2.1mm EP.

The dimensions are described here: https://pdfserv.maximintegrated.com/package_dwgs/21-0139.PDF

However, there is a problem with generated footprint that I don't seem to be able to fix:

Anything I'm missing?