Rename sd_utils to fs_utils, etc

fusee/fusee-secondary/src/fs_utils.c

@@ -0,0 +1,15 @@
+#include <stdio.h>
+#include "fs_utils.h"
+#include "hwinit.h"
+#include "sdmmc.h"
+
+size_t read_from_file(void *dst, size_t dst_size, const char *filename) {
+    FILE *file = fopen(filename, "rb");
+    if (file == NULL) {
+        return 0;
+    } else {
+        size_t sz = fread(dst, 1, dst_size, file);
+        fclose(file);
+        return sz;
+    }
+}