verifiers: File type for fine-grained signature-verification controlling

Let's provide file type info to the I/O layer. This way verifiers
framework and its users will be able to differentiate files and verify
only required ones.

This is preparatory patch.

Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>

grub-core/efiemu/main.c

@@ -187,7 +187,7 @@ grub_efiemu_load_file (const char *filename)
   grub_file_t file;
   grub_err_t err;
 
-  file = grub_file_open (filename);
+  file = grub_file_open (filename, GRUB_FILE_TYPE_GRUB_MODULE);
   if (! file)
     return grub_errno;