radv: Fix rasterization precision bits.

radv: Fix rasterization precision bits.

Note that these limits are exact, not a "precision is at least x",
as texel coords also get snapped to a multiple of this step size
before filtering.

This fixes CTS tests

dEQP-VK.texture.explicit_lod.2d.sizes.31x55_nearest_linear_mipmap_nearest_repeat
dEQP-VK.texture.explicit_lod.2d.sizes.57x35_nearest_linear_mipmap_nearest_repeat

Fixes: f4e499ec791 "radv: add initial non-conformant radv vulkan driver"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109151
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>