i965/gen4: Add support for single layer in alignment workaround

i965/gen4: Add support for single layer in alignment workaround

On gen < 6 one doesn't have level or layer specifiers available
for render and depth targets. In order to support rendering to
specific level/layer, driver needs to manually offset the surface
to the desired slice.
There are, however, alignment restrictions to respect as well and
in come cases the only option is to use temporary single slice
surface which driver copies after rendering to the full miptree.

Current alignment workaround introduces new texture images which
are added to the parent texture object. Texture validation later
on copies the additional levels back to the surface that contains
the full mipmap.
This only works for non-arrayed surfaces and driver currently
creates new arrayed images in vain - individual layers within the
newly created are still unaligned the same as before.

This patch drops this mechanism and instead attaches single
temporary slice into the render buffer. This gets immediately
copied back to the mipmapped and/or arrayed surface just after
the render is done.

Sitting on top of earlier series cleaning up the depth buffer
state, this patch additionally fixes the following piglit tests:

    arb_framebuffer_object.fbo-generatemipmap-cubemap.g965m64
    arb_texture_cube_map.copyteximage cube.g965m64
    arb_texture_cube_map.copyteximage cube.ilkm64
    arb_pixel_buffer_object.texsubimage array pbo.g965m64
    ext_framebuffer_object.fbo-cubemap.g965m64
    ext_texture_array.copyteximage 1d_array.g45m64
    ext_texture_array.copyteximage 1d_array.g965m64
    ext_texture_array.copyteximage 1d_array.ilkm64
    ext_texture_array.copyteximage 2d_array.g45m64
    ext_texture_array.copyteximage 2d_array.g965m64
    ext_texture_array.copyteximage 2d_array.ilkm64
    ext_texture_array.fbo-array.g965m64
    ext_texture_array.fbo-generatemipmap-array.g965m64
    ext_texture_array.gen-mipmap.g965m64

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>