zink: correct depth-stencil format

zink: correct depth-stencil format

When using packed vulkan-formats on little-endian systems, we need to
swap the components for the gallium formats. And since Zink isn't
big-endian safe yet, little-endian is the only endianess we care about
right now.

This fixes a bunch of piglit tests, amongs others:
- spec@arb_depth_texture@depth-level-clamp
- spec@arb_depth_texture@depthstencil-render-miplevels * d=z24
- spec@arb_depth_texture@fbo-depth-gl_depth_component24-blit
- spec@arb_depth_texture@fbo-depth-gl_depth_component24-copypixels
- spec@arb_depth_texture@fbo-depth-gl_depth_component24-drawpixels
- spec@arb_depth_texture@fbo-depth-gl_depth_component24-readpixels

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Fixes: 8d46e35d16e ("zink: introduce opengl over vulkan")