add option NOMSG_ON_SERIAL.

Targets/Bonito2fdev/Bonito/start_cs5536.S

@@ -1321,6 +1321,10 @@ END(hexserial)
 
 LEAF(tgt_putchar)
 	.set noat
+#ifdef NOMSG_ON_SERIAL
+	jr ra
+	nop
+#endif
 	move AT,ra
 #if  (((PCI_IDSEL_VIA686B != 0)||(PCI_IDSEL_CS5536 != 0))&& !defined(HAVE_NB_SERIAL))
 	la	v0, COM1_BASE_ADDR

pmon/dev/ns16550.c

@@ -123,13 +123,22 @@ ns16550 (int op, struct DevEntry *dev, unsigned long param, int data)
 			return nsprogram (dp, dev->freq, data);
 
 		case OP_TXRDY:
+		#ifdef NOMSG_ON_SERIAL
+		return 1;
+		#endif
 			return (inb(&dp->lsr) & LSR_TXRDY);
 
 		case OP_TX:
+		#ifdef NOMSG_ON_SERIAL
+		return 0;
+		#endif
 			outb(&dp->data, data);
 			break;
 
 		case OP_RXRDY:
+		#ifdef NOMSG_ON_SERIAL
+		return 0;
+		#endif
 			return (inb(&dp->lsr) & LSR_RXRDY);
 
 		case OP_RX: