gfxstream: free up hwvulkan_device_t upon driver unloading

Per <hardware/hwvulkan.h>, the hw_device_t::close() function is called
upon driver unloading. The behavior has been like this since Android 10.

Acked-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35561>

src/gfxstream/guest/vulkan/gfxstream_vk_android.cpp

@@ -63,6 +63,11 @@ static int gfxstream_vk_hal_open(const struct hw_module_t* mod, const char* id,
 }
 
 static int gfxstream_vk_hal_close(struct hw_device_t* dev) {
-    /* hwvulkan.h claims that hw_device_t::close() is never called. */
-    return -1;
+    /* the hw_device_t::close() function is called upon driver unloading */
+    assert(dev->version == HWVULKAN_DEVICE_API_VERSION_0_1);
+    assert(dev->module == &HAL_MODULE_INFO_SYM.common);
+
+    hwvulkan_device_t *hal_dev = container_of(dev, hwvulkan_device_t, common);
+    free(hal_dev);
+    return 0;
 }