Improve serial port printing compatibility

When using the ch34x USB2TTL adapter cable, garbled characters
will be printed on the serial console.
Detailed rootcause analysis, please see [1].

Learn the patch and update fsbl binaries and rvos serial port
baud rate settings.

However, according to my test observations, the ch34x chip is still not
stable enough, and there will still be a small period of garbled code
at the beginning of startup, so it is recommended to use FT232.

Link [1]: https://community.milkv.io/t/set-the-baud-rate-to-115200-before-uboot/959

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>

code/os/11-syscall/uart.c

@@ -103,10 +103,18 @@ void uart_init()
 	 * See Datasheet @ https://github.com/milkv-duo/duo-files/tree/main/duo/datasheet
 	 * Chapter 12.2.4.1
 	 * Default UART working clock (UART_SCLK) is XTAL 25MHz.
+	 *
+	 * Strictly follow the TRM formula to calculate,
+	 * divisor = UART_CLOCKRATE / (16 * UART_BAUDRATE)
+	 * DLL = divisor & 0xff;
+	 * DLM = (divisor >> 8) & 0xff;
+	 * In theory, the value obtained by the division calculation
+	 * is approximately 13.56. However, the division result on the computer
+	 * will directly discard the decimal, resulting in 13.
+	 * The loss of accuracy is large. Using 14 has a smaller error.
 	 */
-	int divisor = 25000000 / (16 * 115200);
-	uart_write_reg(DLL, (divisor & 0xff));
-	uart_write_reg(DLM, ((divisor >> 8) & 0xff));
+	uart_write_reg(DLL, 0x0e);
+	uart_write_reg(DLM, 0x00);
 #else
 	#warning "Unsupported Platform!"
 #endif