vulkan: Fix EnumeratePhysicalDeviceGroups()

Fixes CTS failure in dEQP-VK.api.info.instance.physical_device_groups on
Eve (Pixelbook) with Pi.

The Vulkan spec requires that vkEnumeratePhysicalDeviceGroups return
VK_INCOMPLETE when (a) pPhysicalDeviceGroupProperties is not NULL and
(b) *pPhysicalDeviceGroupCount is less than the actual number of groups.

Bug libvulkan/driver.cpp:EnumeratePhysicalDeviceGroups() returned
VK_SUCCESS when (pPhysicalDeviceGroupProperties != NULL &&
*pPhysicalDeviceGroupCount == 0) regardless of the actual number of
groups.

V2: Simplify according to zzyiwei@'s suggestion

Bug: b/114614186
Test: dEQP-VK.api.info.instance.physical_device_groups on eve-arcnext
Change-Id: Ia3067e9d8125ff2b708a4fa674e8283a1f17ba0b