efireloc update to match iPXE elf2efi

[mcb30]

Description

As a developer, I would like wimboot and iPXE to use identical tools for creating PE executables, so that I have only a single tool to maintain.

Acceptance criteria

• [x] wimboot's efireloc.c and iPXE's elf2efi.c are unified into a single tool
• [x] wimboot continues to produce a hybrid 32-bit BIOS and 64-bit UEFI binary

[mcb30]

Implemented in commit a49b707