The EFI boot is handled during the upgrade procedure to be able to boot to the target system. However, as the Legacy Grub bootloader is not migrated automatically during the in-place upgrade, some manual steps are required after the upgrade regarding the EFI boot as well. Follow the official documentation after the upgrade to finish migration to the GRUB 2 bootloader including the steps related to the EFI boot: [link:https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/sec-Upgrading_from_GRUB_Legacy_to_GRUB_2.html].

See the remediation instructions for grub in the preupgrade report as well.
