Increase MAX_CLIP_PLANES to 8
Increase MAX_CLIP_PLANES to 8

This will allow drivers to increase ctx->Const.MaxClipPlanes to 8,
which is required for GLSL-1.30 compliance.

No driver behavior should be affected.  However, many data structures
use MAX_CLIP_PLANES as an array size, so these arrays will get
slightly larger.

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>

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