v3dv: Fix dEQP-VK.info#instance_extensions test
When mesa3d is built without VK_USE_PLATFORM_DISPLAY_KHR definition, dEQP test fails:
dEQP : Test case 'dEQP-VK.info.instance_extensions'..
dEQP : Fail (Extension VK_KHR_get_display_properties2 is missing
dependency: VK_KHR_display)
dEQP : DONE!
Enable KHR_get_display_properties2 only if VK_USE_PLATFORM_DISPLAY_KHR is enabled.