etnaviv: support GL_ARB_seamless_cubemap_per_texture

Passes spec@amd_seamless_cubemap_per_texture@amd_seamless_cubemap_per_texture

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-By: Guido Günther <agx@sigxcpu.org>
10 jobs for !997 with seamless-cube-map in 7 minutes and 56 seconds (queued for 2 seconds)
merge request