serial: imx: add support for loopback mode.

Add the loopback mode support for imx uart driver.

Signed-off-by: Huang Shijie <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/imx.c

···
 	if (readl(sport->port.membase + UCR2) & UCR2_CTS)
 		tmp |= TIOCM_RTS;
 
+	if (readl(sport->port.membase + uts_reg(sport)) & UTS_LOOP)
+		tmp |= TIOCM_LOOP;
+
 	return tmp;
 }
 
···
 			temp |= UCR2_CTS;
 
 	writel(temp, sport->port.membase + UCR2);
+
+	temp = readl(sport->port.membase + uts_reg(sport)) & ~UTS_LOOP;
+	if (mctrl & TIOCM_LOOP)
+		temp |= UTS_LOOP;
+	writel(temp, sport->port.membase + uts_reg(sport));
 }
 
 /*