Set 32bpp as default bit depth instead of 16bpp in usetup

ReactOS doesn't implement mode-testing, instead of that it provides a hardcoded list of common resolutions and bit-depths inside of `txtsetup.sif`, which is used by usetup in first stage.

This patch changes the default entry from vbe_800x600x16 to vbe_800x600x32. While the change is minimal its repercussions are dramatic, specially keeping in mind that most users/testers/reviewers never change the defaults and see the OS in a lower, dithered version.

Let's use saner defaults or many people will keep using ReactOS as if this was 1998.