intel: fix max number of threads used on Ivy Bridge.
intel: fix max number of threads used on Ivy Bridge.

Fix the max number of threads to be used on Ivy Bridge. In particular,
the GEN7_PS_MAX_THREADS_SHIFT offset was wrong, thus causing the GPU
to use half of what was specified.

Signed-off-by: Gwenole Beauchesne <729713629d9640cc095f1c77c692e1881f8093c4@intel.com>

chenxianqin/vaapi-intel-driver,01org/iotg-lin-gfx-va-driver,01org/iotg-lin-gfx-va-driver,halleyzhao/libva-intel-driver-fdo,gbeauchesne/libva-intel-driver,chenxianqin/vaapi-intel-driver,halleyzhao/libva-intel-driver-fdo,01org/iotg-lin-gfx-va-driver,uartie/vaapi-intel-driver,01org/iotg-lin-gfx-va-driver,chenxianqin/vaapi-intel-driver,halleyzhao/libva-intel-driver-fdo,uartie/vaapi-intel-driver,halleyzhao/libva-intel-driver-fdo,uartie/vaapi-intel-driver,gbeauchesne/libva-intel-driver,chenxianqin/vaapi-intel-driver,gbeauchesne/libva-intel-driver,chenxianqin/vaapi-intel-driver,uartie/vaapi-intel-driver,uartie/vaapi-intel-driver,gbeauchesne/libva-intel-driver,gbeauchesne/libva-intel-driver,01org/iotg-lin-gfx-va-driver