serial: add extended Linux baud rate support

This patch extends Linux serial_setup() to support additional
standard baud rates (19200, 230400, 460800, 921600).
Unsupported baud rates now gracefully fallback to 57600.

Signed-off-by: Hank Wang <wanghanchi2000@gmail.com>

Author: WangHanChi

erpc_c/port/erpc_serial.cpp

@@ -103,12 +103,24 @@ int serial_setup(int fd, speed_t speed)
         case 9600:
             speed = B9600;
             break;
+        case 19200:
+            speed = B19200;
+            break;
         case 38400:
             speed = B38400;
             break;
         case 115200:
             speed = B115200;
             break;
+        case 230400:
+            speed = B230400; 
+            break;
+        case 460800:
+            speed = B460800;
+            break;
+        case 921600:
+            speed = B921600;
+            break;
         case 57600:
         default:
             speed = B57600;