x86/kexec: Drop page_list argument from relocate_kernel()

x86/kexec: Drop page_list argument from relocate_kernel()

The kernel's virtual mapping of the relocate_kernel page currently needs
to be RWX because it is written to before the %cr3 switch.

Now that the relocate_kernel page has its own .data section and local
variables, it can also have *global* variables. So eliminate the separate
page_list argument, and write the same information directly to variables
in the relocate_kernel page instead. This way, the relocate_kernel code
itself doesn't need to copy it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>