i965_drv_video: fix BSD batch buffer size.
i965_drv_video: fix BSD batch buffer size.

Some stress cases need a large BSD batch buffer.

gbeauchesne/libva,CyanogenMod/android_hardware_intel_libva,chenxianqin/vaapi-libva,chenxianqin/vaapi-libva,Distrotech/libva,01org/iotg-lin-gfx-libva,CyanogenMod/android_hardware_intel_libva,Distrotech/libva,Distrotech/libva,halleyzhao/libva-fdo,chenxianqin/vaapi-libva,android-ia/hardware_intel_libva,gbeauchesne/libva,halleyzhao/libva-fdo,01org/libva-cros,gbeauchesne/libva,01org/iotg-lin-gfx-libva,zzhhui/libva,android-ia/hardware_intel_libva,zzhhui/libva,01org/libva-cros,01org/libva-cros,pma1/libva,pma1/libva,CyanogenMod/android_hardware_intel_libva,zzhhui/libva,pma1/libva,halleyzhao/libva-fdo,01org/iotg-lin-gfx-libva,android-ia/hardware_intel_libva