radv: fix color conversions for normalized uint/sint formats

radv: fix color conversions for normalized uint/sint formats

The hardware actually rounds before conversion. This now matches
what values are used when performing fast clears vs slow clears.

This fixes a rendering issue with Far Cry 3&4. This also fixes
a bunch of CTS tests that use a 8-bit UNORM format (only when
the 512*512 image size hint is manually disabled).

Cc: "19.0" "19.1" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>