MFC r281169, r293724, r293796, r294029, r294041, r294058
MFC r281169 (by andrew):
Make global variabled only used in this file static
MFC r294058:
Make common boot file_loadraw name parameter const
MFC r294041:
Remove unused reg param from fdt_fixup_memory
MFC r293724:
Enable warnings in EFI boot code
MFC r293796:
Fix typo in libefi.c
MFC r294029:
Only build EFI components on supported compilers
Sponsored by: Multiplay