The following avoids registering unsupported GCN offload devices
when iterating over available ones.  With a Zen4 desktop CPU
you will have an IGPU (unspported) which will otherwise be made
available.  This causes testcases like
libgomp.c-c++-common/non-rect-loop-1.c which iterate over all
decives to FAIL.

libgomp/
	* plugin/plugin-gcn.c (suitable_hsa_agent_p): Filter out
	agents with unsupported ISA.