Silence the shim protocol functions

There are some side effects to output strings in the shim protocol functions
1. If grub2 uses gfx mode, the screen would be distorted when shim prints strings.
2. On some machines, the whole system crashed if shim and grub2 print something at the same time. I don't have a clear clue now, but it can be easily reproduced with OVMF and SHIM_VERBOSE enabled. This patch worked around the issue.

Besides the patch to silence the functions, there are patches to reduce the duplicate code.