i965: set ctx->Const.MaxViewport{Width,Height} to 32k

i965: set ctx->Const.MaxViewport{Width,Height} to 32k

From ARB_viewport_array spec:

" * On GL3-capable hardware the VIEWPORT_BOUNDS_RANGE should be at least
    [-16384, 16383].
  * On GL4-capable hardware the VIEWPORT_BOUNDS_RANGE should be at least
    [-32768, 32767]."

This range is set using ctx->Const.MaxViewportWidth value, so just bump
those constants to 32k for gen7+ which can support OpenGL 4.0.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>