RFR(T/XS) 8235773: Tier3 fails because graalunit tests started to run with ZGC

[Ekaterina Pavlova]

Please review the urgent fix for regression introduced by JDK-8215728.

graalunit tests are part of hotspot_compiler_all_gcs jtreg group and started to fail there.
The tests didn't run before because they had
  @requires vm.opt.final.EnableJVMCI == true

With JDK-8215728 this check was deleted as we don't rely on extra EnableJVMCI flag anymore
but set it explicitly in graal tests.

Not all GCs support JVMCI compiler and in particular ZGC.
The fix removes graaalunit tests from hotspot_compiler_all_gcs similar way it is done for aot_jvmci tests.
Also removed graal unit tests from hotspot_compiler_xcomp group.

@requires vm.jvmci was added to all tests so the tests are not run on platforms which don't support JVMCI.



       JBS: https://bugs.openjdk.java.net/browse/JDK-8235773
    webrev: http://cr.openjdk.java.net/~epavlova//8235773/webrev.00/index.html
   testing: tier1-3

regards,
-katya