r600: correct texture offset for array index lookup

r600: correct texture offset for array index lookup

Correct the array index for TEXTURE_*1D_ARRAY, and TEXTURE_*2D_ARRAY
The standard says the array index is evaluated according to

   floor(z + 0.5)

but RNDNE is sufficient also for the test cases were z is close to 1.5
and it is likely to hit 1.5, the corner case were RNDNE gives a result
different from above formula.

v5: - Use RNDNE instead of ADD 0.5 and FLOOR (Ilia Mirkin)
    - update commit message

Fixes 325 tests from android/cts/master/gles3-master.txt:
  dEQP-GLES3.functional.shaders.texture_functions.texture.*sampler2darray*
  dEQP-GLES3.functional.shaders.texture_functions.textureoffset.*sampler2darray*
  dEQP-GLES3.functional.shaders.texture_functions.texturelod.sampler2darray*
  dEQP-GLES3.functional.shaders.texture_functions.texturelodoffset.*sampler2darray*
  dEQP-GLES3.functional.shaders.texture_functions.texturegrad.*sampler2darray*
  dEQP-GLES3.functional.shaders.texture_functions.texturegradoffset.*sampler2darray*
  dEQP-GLES3.functional.texture.filtering.2d_array.formats.*
  dEQP-GLES3.functional.texture.filtering.2d_array.sizes.*
  dEQP-GLES3.functional.texture.filtering.2d_array.combinations.*
  dEQP-GLES3.functional.texture.shadow.2d_array.*
  dEQP-GLES3.functional.texture.vertex.2d_array.*

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>