forthloader: Don't break BIOS boots...

I thought I tested this scenario, but clearly I failed to. =(

BIOS boots won't have efi-autoresizecons, so trying to use it as a forth
word fails during include. Use evaluate on "efi-autoresizecons" as a string
instead to move any potential errors to runtime- safely after we've already
checked that we're booting UEFI.

Pointy hat to: me
Reported by: cy