shim: use an enum for efi_main's error messages.
shim: use an enum for efi_main's error messages.

Numbering the error messages in efi_main directly was a mistake, and the
following patches just make it more apparent.

This makes it an enum so we don't have to re-number at more than one
place when we add or remove them.

Signed-off-by: Peter Jones <2e0a021e603479ff81838c00c3b770daca4e0214@redhat.com>

rhinstaller/shim,rhinstaller/shim,rhinstaller/shim