v3dv: enable alphaToOne feature

This is another case of a feature that is implemented in the compiler
and that only required that we set the shader key properly from the
pipeline state, which we were already doing.

I verified we pass the tests in dEQP-VK.pipeline.multisample.alpha_to_one.*
(we only support 4x multisampling, so we can only pass a single test there),
however, the tests seem to have a bug by which they always pass, even if
the driver doesn't actually implement alpha to one correctly. I submitted
a fix to Khronos and verified that we also pass the fixed tests (and that
we failed them if we don't actually set te shader key correctly).

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7336>

src/broadcom/vulkan/v3dv_device.c

@@ -685,7 +685,7 @@ v3dv_GetPhysicalDeviceFeatures(VkPhysicalDevice physicalDevice,
       .depthBounds = false, /* Only available since V3D 4.3.16.2 */
       .wideLines = true,
       .largePoints = true,
-      .alphaToOne = false,
+      .alphaToOne = true,
       .multiViewport = false,
       .samplerAnisotropy = true,
       .textureCompressionETC2 = true,