ch552: Use the new hardware CTS signals for UART access

- Use CTS signals to let the FPGA and CH552 signal each other that
    it is OK send UART data.
  - Update the CH552 rx and frame handling logic.
  - Fix minor spelling errors and indentation

hw/usb_interface/ch552_fw/include/debug.c

@@ -137,7 +137,8 @@ void putchar(char c)
     SBUF = c;
 }
 
-char getchar() {
+char getchar(void)
+{
     while(!RI); /* assumes UART is initialized */
     RI = 0;
     return SBUF;
@@ -152,7 +153,8 @@ int putchar(int c)
     return c;
 }
 
-int getchar() {
+int getchar(void)
+{
     while(!RI); /* assumes UART is initialized */
     RI = 0;
     return SBUF;
@@ -198,3 +200,68 @@ void gpio_unset(uint8_t pin)
         break;
     }
 }
+
+uint8_t gpio_get(uint8_t pin)
+{
+    uint8_t ret = 0;
+
+    switch (pin) {
+    case 0x10: // p1.4
+        ret = P1 & 0x10;
+        break;
+    case 0x20: // p1.5
+        ret = P1 & 0x20;
+        break;
+    default: // do nothing, unsupported pin.
+        ret = 0xff;
+        break;
+    }
+
+    return ret;
+}
+
+// Set pin p1.4 to GPIO input mode. (FPGA_CTS)
+void gpio_init_p1_4_in()
+{
+    // p1.4
+    P1_MOD_OC &= ~0x10; // Output Mode: 0 = Push-pull output, 1 = Open-drain output
+    P1_DIR_PU &= ~0x10; // Port Direction Control and Pull-up Enable Register:
+                        //    Push-pull output mode:
+                        //        0 = Input.
+                        //        1 = Output
+                        //    Open-drain output mode:
+                        //        0 = Pull-up resistor disabled
+                        //        1 = Pull-up resistor enabled
+}
+
+// Read status of pin 1.4
+uint8_t gpio_p1_4_get(void)
+{
+    return (P1 & 0x10); // p1.4
+}
+
+// Set pin p1.5 to GPIO output mode. (CH552_CTS)
+void gpio_init_p1_5_out()
+{
+    // p1.5
+    P1_MOD_OC &= ~0x20; // Output Mode: 0 = Push-pull output, 1 = Open-drain output
+    P1_DIR_PU |=  0x20; // Port Direction Control and Pull-up Enable Register:
+                        //    Push-pull output mode:
+                        //        0 = Input.
+                        //        1 = Output
+                        //    Open-drain output mode:
+                        //        0 = Pull-up resistor disabled
+                        //        1 = Pull-up resistor enabled
+}
+
+// Set p1.5 high
+void gpio_p1_5_set(void)
+{
+    P1 |= 0x20; // p1.4
+}
+
+// Set p1.5 low
+void gpio_p1_5_unset(void)
+{
+    P1 &= ~0x20;
+}