We had clamped all UBOs to MAX_UNIFORM_BLOCK_SIZE, when D3D11
allows the underlying buffer to be larger as long as each UBO
binding is still within the max.

Bug: 906683
Bug: angleproject:3388
Change-Id: Id5536302dd73a41c0882fddd77e94f4503f00730
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1837356Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>