Delete some more files
Explicitely define config options
Generalize corebootPkg

It now builds for both IA32 and X64 from the same configuration files,
which are renamed from corebootPkgIa32.* to corebootPkg.* to reflect this.

Also drop OvmfPkgX64.*. I kept these as a reference since I wasn't sure
how large the differences between the architectures are.

Please note that X64 isn't functional yet: The entry point assumes 64bit mode
and the offset problem (with some semi-random number of 0-bytes before the
actual code) actually kills the opcode stream here.