dri/i915: Fix off-by-one in i830 clip region size.

dri/i915: Fix off-by-one in i830 clip region size.

The hardware, like i915, uses an inclusive bounds on min and max for
the drawing rectangle, but we were providing a number for exclusive.
The number of bits used by the hardware only covers this value going
up to the maximum size, so when we programmed 2048 as the maximum
inclusive X, it saw a maximum X of 0 and clipped all rendering.  This
caused rendering failures in gnome-shell.

Fixes piglit fbo-maxsize.

v2: dropped changes to the blitter, which does use an exclusive x2, y2.
    [change by anholt]

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45558
Reviewed-by: Eric Anholt <eric@anholt.net>
NOTE: This is a candidate for release branches.