i965: fix dma_buf import with non-zero offset.

i965: fix dma_buf import with non-zero offset.

Fix eglCreateImage() from a packed dma_buf surface with a non-zero offset
to pixels data. In particular, this fixes support for planar YUV surfaces
when they are individually mapped on a per-plane basis, i.e. when the
OES_EGL_image_external is not used and user application wants to use its
own shader code for composition, or processing on individual plane (OCL).

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>