gallium/winsys/drm: add layer to struct winsys_handle
gallium/winsys/drm: add layer to struct winsys_handle

For exporting a specific layer of an array texture.

Signed-off-by: Christian König <c7ea837d7a46effe4232b086213468b8b31643bf@amd.com>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler