[offload][lit] XFAIL all failing tests on the Level Zero plugin (#174804)
We finally got our buildbot added (to staging, at least) so we want to
start running L0 tests in CI.
We need `check-offload` to pass though, so XFAIL everything failing.
There's a couple `UNSUPPORTED` as well, those are for sporadic fails.
Also make set the `gpu` and `intelgpu` LIT variables when testing the
`spirv64-intel` triple.
We have no DeviceRTL yet so basically everything fails, but we manage to
get
```
Total Discovered Tests: 432
Unsupported : 169 (39.12%)
Passed : 67 (15.51%)
Expectedly Failed: 196 (45.37%)
```
We still don't build the level zero plugin by default and these tests
don't run unless the plugin was built, so this has no effect on most
builds.
---------
Signed-off-by: Nick Sarnie <nick.sarnie@intel.com>