Override static NCM memory allocation

The NCM buffers are only accessed in a single file and under very
limited circumstances.  Use a SDKOVERRIDE to make a weak ncm_device
with no memory usage, and put the TUSB ncd_device inside the lwip_usb
folder.

For apps which don't use NCM, this saves >6K of RAM.  For apps which use
NCM, there should be no change.

Author: earlephilhower

cores/rp2040/sdkoverride/ncm_device.c

@@ -0,0 +1,61 @@
+// Dummy shim to be overridden by lwip_usb_ncm
+#include <Arduino.h>
+#include "tusb_option.h"
+
+#if (CFG_TUD_ENABLED && CFG_TUD_NCM)
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#include "device/usbd.h"
+#include "device/usbd_pvt.h"
+
+#include "../../../pico-sdk/lib/tinyusb/src/class/net/ncm.h"
+#include "../../../pico-sdk/lib/tinyusb/src/class/net/net_device.h"
+
+
+extern bool tud_network_can_xmit(uint16_t size) __attribute((weak));
+bool tud_network_can_xmit(uint16_t size) {
+    return false;
+}
+
+extern void tud_network_xmit(void *ref, uint16_t arg) __attribute((weak));
+void tud_network_xmit(void *ref, uint16_t arg) {
+    return;
+}
+
+extern void tud_network_recv_renew(void) __attribute((weak));
+void tud_network_recv_renew(void) {
+}
+
+extern void netd_init(void) __attribute((weak));
+void netd_init(void) {
+}
+
+extern bool netd_deinit(void) __attribute((weak));
+bool netd_deinit(void) {
+  return true;
+}
+
+extern void netd_reset(uint8_t rhport) __attribute((weak));
+void netd_reset(uint8_t rhport) {
+  (void) rhport;
+}
+
+extern uint16_t netd_open(uint8_t rhport, tusb_desc_interface_t const *itf_desc, uint16_t max_len) __attribute((weak));
+uint16_t netd_open(uint8_t rhport, tusb_desc_interface_t const *itf_desc, uint16_t max_len) {
+    return 0;
+}
+
+extern bool netd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes) __attribute((weak));
+bool netd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes) {
+    return false;
+}
+
+extern bool netd_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request_t const *request) __attribute((weak));
+bool netd_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request_t const *request) {
+    return false;
+}
+
+#endif // ( CFG_TUD_ENABLED && CFG_TUD_NCM )