gpu: Add export.h as required to drivers/gpu files.

They need this to get all the EXPORT_SYMBOL variants and THIS_MODULE

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 3830e9e..cb3794a 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -40,6 +40,7 @@
 #include <linux/slab.h>
 
 #include <linux/vgaarb.h>
+#include <linux/export.h>
 
 /* Access macro for slots in vblank timestamp ringbuffer. */
 #define vblanktimestamp(dev, crtc, count) ( \