boot: Move console declarations to missing_efi.h
These were added to eficonex.h in gnu-efi 3.0.13. Let's move them to missing_efi.h behind an appropriate guard to fix the build with recent versions of gnu-efi.
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These were added to eficonex.h in gnu-efi 3.0.13. Let's move them to missing_efi.h behind an appropriate guard to fix the build with recent versions of gnu-efi.