i965/gen7: Fix depth buffer rendering to tile offsets.

i965/gen7: Fix depth buffer rendering to tile offsets.

Previously, we were saying that everything from the starting tile to
region width+height was part of the limits of our depthbuffer, even if
the tile was near the bottom of the depthbuffer.  This mean that our
range was not clipping to buffer buonds if the start tile was anything
but the start of the buffer.

In bebc91f0f3a1f2d19d36a7f1a4f7c992ace064e9, this was changed to
saying that we're just rendering to a region of the size of the
renderbuffer.  This is great -- we get a range that should actually
match what we want.  However, the hardware's range checking occurs
after the X/Y offset addition, so we were clipping out rendering to
small depth mip levels when an X/Y offset was present.  Just add
tile_x/y to the width in that case -- the WM won't produce negative
x/y values pre-offset, so we just need to get the left/bottom sides of
the region to cover our buffer.

Fixes the following Piglit regressions on gen7:
    spec/ARB_depth_buffer_float/fbo-clear-formats
    spec/ARB_depth_texture/fbo-clear-formats
    spec/EXT_packed_depth_stencil/fbo-clear-formats

NOTE: This is a candidate for the 8.0 branch.