Fix EGL render tests on 5551.
Fix EGL render tests on 5551.

- Disable dithering since one-bit alpha dithering cannot be verified.
- Avoid generating narrow triangles.

Bug: 20176678
Change-Id: Ib3372011bda3a99dae51698215e13b881926929b

KhronosGroup/VK-GL-CTS,googlestadia/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,chadversary/deqp,geekboxzone/mmallow_external_deqp,googlestadia/VK-GL-CTS,KhronosGroup/Vulkan-CTS,geekboxzone/mmallow_external_deqp,geekboxzone/mmallow_external_deqp,KhronosGroup/VK-GL-CTS,chadversary/deqp,googlestadia/VK-GL-CTS,chadversary/deqp,chadversary/deqp,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,googlestadia/VK-GL-CTS,KhronosGroup/Vulkan-CTS,chadversary/deqp,KhronosGroup/Vulkan-CTS,googlestadia/VK-GL-CTS,googlestadia/VK-GL-CTS,geekboxzone/mmallow_external_deqp,geekboxzone/mmallow_external_deqp,geekboxzone/mmallow_external_deqp,chadversary/deqp