In shaders/ directory we got Intel specific information. As igt
is a project for more vendors, let's move this directory to
lib/i915.

v2: Changed shaders directory path in library files comments.

Signed-off-by: Katarzyna Dec <katarzyna.dec@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Petri Latvala <petri.latvala@intel.com>
Cc: Kalamarz Lukasz <lukasz.kalamarz@intel.com>
Cc: Antonio Argenziano <antonio.argenziano@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>