espressif: Allow -DENABLE_JTAG=0 to force JTAG off

With the Kaluga devkit, the camera interferes with the JTAG function.
However, having DEBUG turned on e.g., to get extended debug information
on the UART debug connection remains useful.

Now, by arranging to add to CFLAGS += -DDEBUG -DENABLE_JTAG=0, this
configuration is easy to achieve.

ports/espressif/supervisor/port.c

@@ -127,7 +127,11 @@ safe_mode_t port_init(void) {
     heap = NULL;
     never_reset_module_internal_pins();
 
-    #if defined(DEBUG)
+    #ifndef DEBUG
+    #define DEBUG (0)
+    #endif
+
+    #if DEBUG
     // debug UART
     #ifdef CONFIG_IDF_TARGET_ESP32C3
     common_hal_never_reset_pin(&pin_GPIO20);
@@ -138,7 +142,11 @@ safe_mode_t port_init(void) {
     #endif
     #endif
 
-    #if defined(DEBUG) || defined(ENABLE_JTAG)
+    #ifndef ENABLE_JTAG
+    #define ENABLE_JTAG (defined(DEBUG) && DEBUG)
+    #endif
+
+    #if ENABLE_JTAG
     // JTAG
     #ifdef CONFIG_IDF_TARGET_ESP32C3
     common_hal_never_reset_pin(&pin_GPIO4);