intel: add stub_gpu tool

intel: add stub_gpu tool

Run shaderdb like this :

   intel_stub_gpu -p bxt ./run ./shaders/*

List of platform names is available from
gen_device_name_to_pci_device_id() (src/intel/dev/gen_device_info.c).

v2: Add missing getparam support
    Raise max soft limit of file descriptors

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4594>