iris: support INTEL_NO_HW environment variable

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/gallium/drivers/iris/iris_batch.c

@@ -491,7 +491,7 @@ submit_batch(struct iris_batch *batch)
          (uintptr_t)util_dynarray_begin(&batch->exec_fences);
    }
 
-   int ret = drm_ioctl(batch->screen->fd,
+   int ret = batch->screen->no_hw ? 0 : drm_ioctl(batch->screen->fd,
                        DRM_IOCTL_I915_GEM_EXECBUFFER2,
                        &execbuf);
    if (ret != 0) {

src/gallium/drivers/iris/iris_screen.c

@@ -560,6 +560,9 @@ iris_screen_create(int fd)
    screen->devinfo.timestamp_frequency =
       iris_getparam_integer(screen, I915_PARAM_CS_TIMESTAMP_FREQUENCY);
 
+   if (getenv("INTEL_NO_HW") != NULL)
+      screen->no_hw = true;
+
    screen->bufmgr = iris_bufmgr_init(&screen->devinfo, fd);
    if (!screen->bufmgr)
       return NULL;

src/gallium/drivers/iris/iris_screen.h

@@ -52,6 +52,8 @@ struct iris_screen {
    /** PCI ID for our GPU device */
    int pci_id;
 
+   bool no_hw;
+
    /** Global program_string_id counter (see get_program_string_id()) */
    unsigned program_id;