cmd, consensus, eth: split ethash related config to it own (#15520)

* cmd, consensus, eth: split ethash related config to it own

* eth, consensus: minor polish

* eth, consenus, console: compress pow testing config field to single one

* consensus, eth: document pow mode

consensus/ethash/algorithm_test.go

@@ -703,8 +703,7 @@ func TestConcurrentDiskCacheGeneration(t *testing.T) {
 
 		go func(idx int) {
 			defer pend.Done()
-
-			ethash := New(cachedir, 0, 1, "", 0, 0)
+			ethash := New(Config{cachedir, 0, 1, "", 0, 0, ModeNormal})
 			if err := ethash.VerifySeal(nil, block.Header()); err != nil {
 				t.Errorf("proc %d: block verification failed: %v", idx, err)
 			}