FileSys/Kernel: Implement SetSize service call for File objects.

src/core/file_sys/file_sdmc.cpp

@@ -75,6 +75,17 @@ size_t File_SDMC::GetSize() const {
     return static_cast<size_t>(file->GetSize());
 }
 
+/**
+ * Set the size of the file in bytes
+ * @param size New size of the file
+ * @return true if successful
+ */
+bool File_SDMC::SetSize(const u64 size) const {
+    file->Resize(size);
+    file->Flush();
+    return true;
+}
+
 /**
  * Close the file
  * @return true if the file closed correctly