i965/miptree: Layout 1D Array as 2D Array with height of 1

i965/miptree: Layout 1D Array as 2D Array with height of 1

1D array miptrees were being laid out as a 2D texture with 1 slice.
This happened due to the mesa core storing the 1D array slice count in
the height field. On Intel hardware, we want to create a 2D array with
a height of 1 for the 1D array case.

Fixes assertion failure in piglit (gen6, gen8):
spec/glsl-1.30/execution/tex-miplevel-selection textureOffset 1DArrayShadow

In release builds of Mesa, this test was observed to cause a GPU hang
on gen8.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: "10.2" <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81450
Tested-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>