check that intel-gen4asm tool is actually present
check that intel-gen4asm tool is actually present

intel-gen4asm tool has to be present on the host tools so that
it can actually be used. Cross compiling shows problems when the
gpu-tools version is met but the tool is not available on the PATH

So, first check that the tool is available and later check for version
before defining HAVE_GEN4ASM.

Signed-off-by: Daniel Charles <daniel.charles@intel.com>
(cherry picked from commit 038097c00ad7b4f2e0fd572ee20f255dd378b5cb)

Conflicts:

	configure.ac

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