i965: Allow import/export of ARGB1555 images

To my knowledge, this fixes no tests. I simply wrote the patch for
completeness as a follow-up to the previous two patches.

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
diff --git a/src/mesa/drivers/dri/i965/intel_screen.c b/src/mesa/drivers/dri/i965/intel_screen.c
index e1c3c19..d0e3ac6 100644
--- a/src/mesa/drivers/dri/i965/intel_screen.c
+++ b/src/mesa/drivers/dri/i965/intel_screen.c
@@ -230,6 +230,9 @@
    { __DRI_IMAGE_FOURCC_XBGR8888, __DRI_IMAGE_COMPONENTS_RGB, 1,
      { { 0, 0, 0, __DRI_IMAGE_FORMAT_XBGR8888, 4 }, } },
 
+   { __DRI_IMAGE_FOURCC_ARGB1555, __DRI_IMAGE_COMPONENTS_RGBA, 1,
+     { { 0, 0, 0, __DRI_IMAGE_FORMAT_ARGB1555, 2 } } },
+
    { __DRI_IMAGE_FOURCC_RGB565, __DRI_IMAGE_COMPONENTS_RGB, 1,
      { { 0, 0, 0, __DRI_IMAGE_FORMAT_RGB565, 2 } } },