Add example to boot M4 code from file + SDRAM

Author: facchinm

libraries/RPC/examples/BootM4_from_SDRAM/BootM4_from_SDRAM.ino

@@ -0,0 +1,59 @@
+#include "SDRAM.h"
+#include "QSPIFBlockDevice.h"
+#include "MBRBlockDevice.h"
+#include "FATFileSystem.h"
+#include "PluggableUSBMSD.h"
+
+QSPIFBlockDevice root(PD_11, PD_12, PF_7, PD_13,  PF_10, PG_6, QSPIF_POLARITY_MODE_1, 40000000);
+mbed::MBRBlockDevice ota_data(&root, 2);
+mbed::FATFileSystem ota_data_fs("fs");
+
+void USBMSD::begin()
+{
+}
+
+USBMSD MassStorage(&root);
+
+long getFileSize(FILE *fp) {
+  fseek(fp, 0, SEEK_END);
+  int size = ftell(fp);
+  fseek(fp, 0, SEEK_SET);
+
+  return size;
+}
+
+void setup() {
+  // put your setup code here, to run once:
+  Serial.begin(115200);
+  while (!Serial);
+
+  SDRAM.begin(0);
+
+  int err = ota_data_fs.mount(&ota_data);
+  if (err) {
+    Serial.println("Please run PortentaWiFiFirmwareUpdater once");
+    while (1) {
+      delay(10000);
+    }
+  }
+
+  // Copy M4 firmware to SDRAM
+  FILE* fw = fopen("/fs/fw.bin", "r");
+  if (fw == NULL) {
+    Serial.println("Please copy a firmware for M4 core in the PORTENTA mass storage");
+    Serial.println("When done, please unmount the mass storage and reset the board");
+    MassStorage.begin();
+    while (1) {
+      delay(10000);
+    }
+  }
+  fread((uint8_t*)CM4_BINARY_START, getFileSize(fw), 1, fw);
+  fclose(fw);
+
+  bootM4();
+}
+
+void loop() {
+  // put your main code here, to run repeatedly:
+  delay(10000);
+}