mesa/st: hardcode the viewport bounds range

mesa/st: hardcode the viewport bounds range

The bound range is disconnected from the viewport dimensions. This is
the relevant bit from glViewportArray:

"""
The location of the viewport's bottom left corner, given by (x, y) is
clamped to be within the implementaiton-dependent viewport bounds range.
The viewport bounds range [min, max] can be determined by calling glGet
with argument GL_VIEWPORT_BOUNDS_RANGE. Viewport width and height are
silently clamped to a range that depends on the implementation. To query
this range, call glGet with argument GL_MAX_VIEWPORT_DIMS.
"""

Just set it to +/-16384, as that is the minimum required by
ARB_viewport_array and the value that all current drivers provide.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Dave Airlie <airlied@redhat.com>