If specialization constant is used, driver uniform data structure should
be reduced to minimum to increase cache locality.

Bug: b/175479076
Change-Id: I1fc50666542c6763c60bfe011cde5bc77ccc08e1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2588549Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Charlie Lao <cclao@google.com>