gav1: Increase max supported resolution to 4096x4096

This brings the AV1 decoder in line with other modern codecs. It
also helps the software decoder to decode most practical AVIF
images.

Bug: 141654151
Test: Media CTS tests still pass
Merged-In: Iedbd41f2336585a5d769b1d9c94e40d6e0d155ed
Change-Id: I394e3e652bdb9f4cf5e9f7767d2d31e09aaf7381