Add fw_path variable to detect config file on efi

Add fw_path variable to detect config file on efi

This patch makes grub look for its config file on efi where the app was
found.

Resolves: rhbz#857936, rhbz#1616395
Co-authored-by: Matthew Garrett
Co-authored-by: Javier Martinez Canillas <javierm@redhat.com>
Co-authored-by: Robbie Harwood <rharwood@redhat.com>
Signed-off-by: Paulo Flabiano Smorigo <pfsmorigo@br.ibm.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Robbie Harwood <rharwood@redhat.com>
Gbp-Pq: Topic network
Gbp-Pq: Name add-fw_path-variable-to-detect-config-file-on-efi.patch