Add support for 64-bit PowerPC kernels to be directly loaded by kexec, which
is used as the bootloader on a number of PPC64 platforms. This involves the
following pieces:
- Making the first instruction a valid kernel entry point, since kexec ignores the ELF entry value. This requires a separate section and linker magic to prevent the linker from filling the beginning of the section with stubs.
- Adding an entry point at 0x60 past the first instruction for systems lacking firmware CPU shutdown support (notably PS3).
- Linker script changes to support the above.
MFC after: 1 month